PHOTOPROTECTIVE COMPOSITIONS AND FILMS, AND A PREPARATION METHOD The present invention relates to compositions and to methods for photoprotecting various materials using particles of photonic material, in particular particles having a polymeric multilayer interference structure obtained from photonic gels. Furthermore, the present invention relates to compositions and to methods of treating human keratinous material. Prior art Current photoprotective compositions use combinations of various screening agents, especially soluble or insoluble organic screens. The absorption spectrum of each of said screens is rarely broad enough to cover the whole UV spectrum, and combinations are necessary. Further, a large number of soluble organic screens may cause compatibility problems with the ingredients usually contained in them, especially as a result of interactions with other organic screens or with active molecules such as antioxidants or vitamins, and their photcstability may not be encirely satisfactory. Many patents are concerned with solving this problem - an indication that this problem crops up repeatedly. Many non-cosmetic industry sectors also use uv screens to photoprotect various materials against the effects of UV radiation, in particular solar radiation. This is particularly true of paint, ink, or protective coating formulations for applying to substances that are permanently exposed to uv radiation, such as construction materials, materials used in the automobile industry, or plastics packaging materials. In particular, UV screens are being developed for colorant formulations that need to be transparent, photostable, compatible with the usual ingredients contained in said formulations, and effective in providing the looked-for color with resistance to light. Similar considerations apply with polymer compositions used in particular in the manufacture of plastics materials that are stable on storage; they need UV light screens to be developed that are particularly- adapted to the methods of manufacturing and transforming polymers, and in particular they need to he able to tolerate the high temperatures used in extrusion. In the natural fiber and/or artificial fibyr and/or synthetic fiber industry, broad spectrum photostable UV screens are being developed that are compatible with methods of manufacturing said fibers, in particular in the context of the manufacture of fibers made of polyamide such as nylon, which are resistant to high temperatures and can incorporate UV protection during extrusion. Further, UV screens are being developed that have good affinity, good adhesion to fibers, and thus in particular can provide good resistance upon frequent washing. The UV screens being developed must also provide both good protection of the textile fibers and also of the skin and other human keratinous material in contact with said fibers. The mineral or organic glass industry, in particular for glass used in ophthalmology, is developing UV screens that need to have a broad spectrum (active in the UVA and in the UV3 regions), and that are photostable, transparent, and compatible with the various techniques for treating glass, such as methods of keying onto the glass matrix or applying a photoprotective coating, for example with polycarbonate glass. Interference materials constituted by a multilayer structure may be used as screening agents. With films having a polymeric multilayer interference structure, the layers may number up to several hundred, for example. Such films may be produced by extrusion, are usually transparent, and are several hundred µm [micrometer] thick. The use of a metal layer, for example of TiO2 or ZnO, can produce greater differences in refractive index and can reduce the number of layers constituting the film. However, films using that technology nay become opaque to visible light and may also prove to be fairly rigid. In a variation, when the films are thick and have a large number of layers, their efficiency may be significantly reduced when they are fragmented into particles. Because of the great, thickness of the films, "edge effects" may very substantially reduce the production of interference. The use of holographic pigments in order to produce a reflection in the UV spectrum is known from application FR 2 921 559. Application FR 2 888 491 discloses a photoprotective composition comprising a screening agent having a multilayer interference structure, the screening agent comprising alternating high refractive index layers and low refractive index layers. "Photonic materials" or "photonic crystals" are known from application US 2009/0086208 that are constituted by a periodic arrangement of at lease two polymeric portions having different dielectric constants. In particular, those polymeric photonic materials contain at least one polymeric portion that is capable, under the influence of an altering stimulus, of producing a change in at least one physical, chemical, or dielectric characteristic including the dimension, shape, dielectric constant, refractive index, color, or other parameter. That change results in modifying a wavelength of electromagnetic radiation diffracted by the photonic material. A photonic gel is a film having a polymeric multilayer structure that may comprise a block polymer that spontaneously forms a periodic lamellar structure during deposition onto a support. Such a material may have interference properties, for example when it is brought into contact with a swelling agent. Photonic gels are known from publications by B. Thomas: Nat Mat Vol 6, 957-96 0, 2008 and J Am Cham soc 2009, 131, 7538 - 7539. There is a need to benefit from novel UV light screening systems adapted to photoprotecting materials such as those mentioned above. There is a need to benefit from non-soluble screening materials that can be used to cover the UVA and/or UVB spectrum, that are completely harmless, inert as regards the environment, are photostable and not photoreactive, that do not have compatibility problems with the other constituents of the compositions containing their., and that do not modify the mechanical properties of the materials of packaging materials in a negative manner. There is a need to benefit from coloring effect materials that are completely harmless, inert as regards the environment, photostable, and not photoreactive, that do not have compatibility problems with the other constituents of the compositions containing them, and that do not modify the mechanical properties of packaging materials in a negative manner, There is also a need to have available polymeric films with a multi-portion structure, in particular having a polymeric multilayer interference structure, with optical properties that are only slightly affected or are unaffected when they are fragmented into particles. The invention, which is intended to satisfy same or all of the needs mentioned above, provides the use of particles of photonic material, in particular particles having a polymeric multilayer interference structure obtained from photonic materials, in particular photonic gels. Summary "Photoprotective™ application Photoprotective compositions ana films In first exemplary embodiments the inven.tion provides a photoprotective composition, in particular a cosmetic, including particles of photonic material. The particles o£ photonic material may in particular be particles having a polymeric multilayer interference structure with at least two layers comprising a polymer. Said polymer may be an amphophilic polymer defining at least two layers of said structure. In other words, at least two layers of said structure may be formed by an amphophilic polymer. In the context of the invention, the term "photoprotective composition" is used to mean a composition that is capable of protecting any material, in particular human keratinous materials, against UV radiation. In particular it has a transmission factor, measured before application to said material, that is less than or equal to 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, or even more preferably less than or equal to 1%, for at least one wavelength in the range 2 50 nm no 400 nm, more preferably over the whole of said range. Screening is much better when the transmission factor over the range 250 ran to 400 nm is low. In the context of the invention, the term "photonic material" is used for a polymeric material comprising a plurality of different portions arranged in a periodic manner, capable of interfering with electromagnetic radiation and of modifying it, with at least a first and a second portion each having a respective dielectric constant and a respective abiliry to modify the electromagnetic radiation dimensionally by at least 5 nm such that the portions define a ratio of dielectric constants of at least 1 for a continuous wavelength range from 10 nm to 10 micrometers when subjected to an altering stimulus. In the context of the invention, the term "polymeric multilayer interference structure" is used for a stack of at least two layers of polymer, preferably more than two layers, the stack being capable of producing interference, for example in order to screen UV, and for example to provide protection against UVA, thereby limiting browning of the skin, and/or to produce a color and/or to lighten the complexion and/or to modify the spectral reflectance, depending on the application. The interference may provide the polymeric multilayer interference structure with a transmission spectrum including one or more transmission minima or a reflection spectrum including one or more reflection peaks in the wavelength range 250 nm to 800 nm. The term "amphiphilic polymer" should be understood to mean a polymer comprising a hydrophilic group and a hydrophobic group. An amphophilic polymer may, for example, be a block copolymer comprising at least one hydrcphilic block and at least one hydrophobic block. According to other exemplary embodiments the invention provides a composition, in particular a cosmetic composition, including particles of photonic material, in particular particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it. The polymer is, for example, an amphophilic polymer, for example as defined above, The term "polymer having a UV screen within it" should be understood to mean that particles having UV screening properties and that are distinct from the groups forming said polymer are imprisoned in the structure formed by said polymer. In other words, the UV screen is present in addition to said polymer in the structure formed thereby. According to other exemplary embodiments the invention provides a film that photoprotects against solar UV radiation, for application to a material, in particular to human keratinous materials, the film including a photonic material, in particular a multilayer interference structure screening solar UV radiation, in which at least two layers comprise an amphophilic polymer. The amphophilic polymer may define at least two layers of the polymeric multilayer interference structure screening solar UV radiation. In other words, as with the particles, at least two layers of the structure may be formed by an amphophilic polymer. According to other exemplary embodiments the invention provides a photoprotective film for application to a material, in particular to human keratinous materials, comprising a photonic material, more particularly a polymeric multilayer interference structure, comprising a polymer having a UV screen within it for example as defined above. The photoprotective films described above may be applied to a material, for example selected from materials manufactured from at least one synthetic or natural polymer, organic or mineral glasses, and materials comprising at least natural fibers and/or artificial fibers and/or synthetic fibers such as textiles or papers. The formulations for the photoprotective films are selected in such a manner that they have a transmission factor, measured before application to the material of interest, in particular to keratinous materials, that is less than or equal to 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, or even better preferably less than or equal to 1%, for at least one wavelength in the range 2 50 nm to 400 nm, more preferably over the whole of said range. Screening is even better when the transmission factor over the range 25 0 run to 400 nm is low. Preparation methods In other exemplary embodiments, the invention provides a method of preparing a photoprotective composition as described above, said method comprising: a) a step of bringing a swelling agent into contact with a photonic material, in particular having a polymeric multilayer structure with at least two layers comprising an amphophilic polymer; b) a step of fragmenting a film of photonic material, in particular a film having a polymeric multilayer structure in which at least two layers comprise an amphiphilic polymer, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of 100 µm or less and/or with a smallest dimension of 100 nm or more; and c) a step of dispersing the particles of photonic material, in particular particles having a polymeric multilayer interference structure obtained after carrying out steps a) and b) , in. a suitable medium; step b) being carried out before or after step a) . According to other exemplary embodiments, the invention provides a method of preparing a photoprotective composition as described above, said method comprising: a) a step of bringing a swelling agent including a dissolved UV screen into contact with a photonic material, in particular a photonic material having a polymeric multilayer structure; b) a step of fragmenting a film o£ photonic material, in particular a film having a polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of 10 0 µm or less and/or with a smallest dimension of 100 nm or mere; and c) a step of dispersing the particles of photonic material, in particular particles having a polymeric multilayer interference structure obtained after carrying out steps a} and b), in a suitable medium; step b) being carried out before or after step a). The photoprotective compositions prepared by the methods described above may bs photoprotective and cosmetic compositions, the dispersion of step c) then being carried out in a cosmetically acceptable medium. Uses of photoprotective compositions and films According to other exemplary embodiments the invention provides a method of photoprotecting a material against solar UV radiation, the method comprising the steps consisting in: - treating said material with a photoprotective composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer; or - integrating at least said composition into said material According to other exemplary embodiments the invention provides a non-therapeutic and in particular a cosmetic method of photoprotecting human keratinous materials against solar UV radiation, the method comprising the step consisting in applying to the human keratinous materials a photoprotective cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising ar. amphiphilic polymer. Other exemplary embodiments of the invention also provide a physiologically acceptable, in particular a cosmetic composition, for use in a method of phoroprotection of human keratinous material against solar UV radiation, in particular in a method for reducing the risk of apparition of a skin cancer, Wherein said composition includes particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer. Unless, otherwise specified, said composition may present all the features of the cosmetic compositions according -o the present invention. According to other exemplary embodiments the invention provides a method of photopratecting an ink, a paint, or a coating, the rnethod comprising the step of incorporating into said ink or said painc or said coating at. least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer. According to other exemplary embodiments the invention provides a method of photoprotecting a material manufactured from at least one synthetic or natural polymer, the method comprising the step of: - treating said polymer with a composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer; or integrating said composition into said material. According to other exemplary embodiments the invention provides a method of photoprotecting an organic or mineral glass comprising the step of: - treating said glass with at least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising 3n amphiphilic polymer; or integrating said composition into said glass. According to ocher exemplary embodiments the invention provides a method of photoprotecting a material comprising at least natural fibers and/or artificial fibers and/or synthetic fibers such as textiles or papers, the method comprising the step of: - creating said material with at least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphophilic polymer; or integrating said composition into said material. According to other exemplary embodiments the invention, provides a method of photoprotecting a material against solar UV radiation, the method comprising the step consisting of: - treating said material winh a photoprotective composition including particles cf photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphophilic polymer as defined above; or - integrating at least said composition into said material. According to other exemplary embodiments the invention provides a non-therapeutic, and in particular a cosmetic, method of photoprotecting human keratinous materials against sola.r UV radiation, the method comprising the step consisting in applying to human keratinous materials a photoprotective cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphophilic polymer as defined above. Other exemplary embodiments of the invention also provide a physiologically acceptable, in particular a cosmetic composition, for use in & method of photoprotection of human. keratinous material against solar UV radiation, in particular in a method for reducing the risk of apparition of a skin cancer. Wherein said composition particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphiphilic polymer as defined above. Unless, otherwise specified, said composition may present all the features of the cosmetic compositions according to the present invention. According to other exemplary embodiments the invention provides a method of photoprotecting an ink, a paint or a coating, the method comprising the step of incorporating into said ink or paint or said coating at least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphiphilic polymer as defined above. According to other exemplary embodiments the invention provides a method of photoprotecting a material manufactured from at least one synthetic or natural polymer, the method comprising the step of: - treating said polymer with a composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a uv screen within it, for example an amphiphilic polymer as defined above; or integrating said composition into said material. According to other exemplary embodiments the invention provides a method of photoprotecting an organic or mineral glass comprising the step of: - treating said glass with at least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphiphilic polymer as defined above; or integrating said composition into said glass. According to other exemplary embodiments the invention provides a method of photoprotecting a material comprising at least natural fibers and/or artificial fibers and/or synthetic fibers such as textiles or papers, the method comprising the step of: - treating said material with at least one composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it, for example an amphiphilic polymer as defined above-, or integrating said composition in~o said material. By wayr of example, the compositions and films used in the photoprotection methods of the invention have an SPF index, measured before application to the keratinous materials, of at least 10, more preferably 15, more preferably at least 30, 45, or 60. The SPF (Sun Screen Protection Factor) index is defined in the article "A new substrate to measure sunscreen protection factors throughout the ultraviolet spectrum", J Soc Cosmet Chem, 40, 127 - 133 (May/June 1969). 'Fluorescence" application Compositions and films In other exemplary embodiments the invention provides a cosmetic composition including particles, of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a fluorescent agent within it, for example as defined above. The polymer may, for example, be an amphiphilic polymer. The term "polymer having a fluorescent agent within it" is used to mean that particles having fluorescent properties and that are distinct from the groups forming said polymer are imprisoned in the structure formed by said polymer. In other words, the particles having fluorescent properties are present in addition to said polymer in the structure formed thereby. Preparation method In other exemplary embodiments the invention provides a method of preparing a cosmetic composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, comprising a polymer having a fluorescent agent within it, for example as defined above, said method comprising: a) a step of bringing a swelling agent includinging a dissolved fluorescent agent into contact with a photonic material, in particular having a polymeric multilayer structure; b) a step of fragmenting a film of photonic material, in particular a film having said polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of 100 urn or less and/or with a smallest dimension of 10 0 ran or more; and c) a s~ep of dispersing the particles of photonic material, in particular particles having a polymeric multilayer interference structure obtained after carrying out steps a) and b), in a cosmetically acceptable medium; step b) being carried out before or after step a). Uses of compositions and films In other exemplary embodiments the invention provides a method of lightening human karatinous materials, -he raerhod comprising the step consisting in applying a cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a fluorescent agent within it, for example as defined above. According to other exemplary embodiments the invention provides a film for lightening the complexion, for application to human keratinous materials, comprising a photonic material, more particularly a polymeric multilayer interference structure, comprising a polymer having a fluorescent agent within it, for example as defined above. "Coloring1 applica t i on Compositions and films In other exemplary embodiments the invention provides a cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, producing a visible color. According to other exemplary embodiments the invention provides a cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a coloring agent within it, for example as defined above. The term "polymer having a coloring agent within it" is used to mean that a coloring agent that is distinct from the groups forming said polymer is imprisoned in the structure formed by said polymer. In other words, the coloring agent is present in addition to said polymer in the structure formed thereby. According to other exemplary embodiments the invention provides a. film for makeup, for example to even out the complexion, for application to human keratinous materials, the film including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, producing a visible color. According to other exemplary embodiments the invention provides a film for makeup, for example to even out the complexion, for application to human keratinous materials, the film including a photonic material structure, in particular a polymeric multilayer interference structure, comprising a polymer having a coloring agent within it. The particles having a polymeric muirilayer interference structure may include an amphiphilic polymer as defined above. Preparation wet hods in other exemplary embodiments the invention provides a method of preparing a cosmetic composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, for example comprising an amphiphilic polymer, producing a visible color, said method comprising: a) a step of bringing a swelling agent into contact with a photonic material, in particular having a polymeric multilayer structure; b) a step of fragmenting a film of photonic material, in particular a film having a polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of 10D urn or less and/or with a smallest- dimension of 100 ran or more; and c) a step of dispersing said particles obtained after carrying out steps a) and b) in a cosmetically acceptable medium; step b) being carried out before or afrer step a). According to other exemplary embodiments zhe invention provides a method of preparing a cosmetic composition including particles of photonic material, in particular parricles having a polymeric multilayer interference structure, comprising a polymer having a coloring agenc within it, for example as defined above, said method comprising: a) a step of bringing a photonic material, in particular having a polymeric multilayer structure, into contact with a swelling agent comprising a dissolved coloring agent; b) a step of fragmenting a film of photonic material, in particular a film having a polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of 100 µm or less and/or with a smallest dimension of 100 nm or more; and c) a step of dispersing said particles obtained after carrying out steps a) and b} in a cosmetically acceptable medium; step b) being carried out before or afcer step a). Uses of compositions and films In other exemplary embodiments the invention- provides a method of making up, for example to even out the complexion, the method comprising the step consisting in applying to human keratinous materials a cosmetic composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, for example comprising an amphophilic polymer as defined above, producing a visible color, said method possibly further comprising a step of selecting a composition, as a function of the color and/or the spectral reflectance of the keratinous materials to be created. According to other exemplary embodiments che invention provides a method of making up, for example tc even out the complexion, the method comprising the suep consisting in applying to human keratinous materials a cosmetic composition including particles of photonic material, more particularly particles having a polymeric multilayer interference structure, comprising a polymer having a coloring agent within it, for example an amphiphilic polymer as defined above, sa^id method possibly further comprising a step of selecting the composition as a function of the color and/or the spectral reflectance of the keratinous materials to be treated. Photonic materials and polymeric multilayer interference structures The particular structural arrangement of the various portions of the material and the dielectric constants of said portions may result in reflection, in at least one direction, of electromagnetic radiation of a particular frequency directed onto the material. The structural arrangement of the various portions of material and the dielectric constants of said portions may form photonic materials that diffract or reflect light about a particular frequency or frequencies. In particular, the polymeric photonic materials contain at least one polymeric portion that is capable of producing a change in at least one physical, chemical, or dielectric characteristic including the dimension, shape, dielectric constant, refractive index, color, or other parameters by means of an altering stimulus. This change has the result of modifying a wavelength of electromagnetic radiation diffracted by the photonic material. As an example, a change in dimension (i.e. volume change) may be produced by swelling of one of the portions of the photonic material my means of a solvent type swelling agent. The dimensional change may modify the structural arrangement of the photonic material and as a result the dielectric constant of one of the portions of the material, or it may modify the electromagnetic radiation reflected hy the photonic material. As an example, a modification of the optical properties nay in particular be due to a periodic type spacing between similar portions. The photonic material may comprise a firs:: portion that is reactive to an altering stimulus producing a change in volume or another dimension and a second portion that is non reactive or that is reactive to another type of stimulation. Photonic materials or photonic crystals are capable of diffracting and/or reflecting electromagnetic radiation over a wide range of wavelengths including the visible, ultraviolet, infrared, and microwave wavelengths. In some circumstances, they may diffract electromagnetic radiation with a wavelength lying in the range 100 run to 1600 run. In other circumstances, photonic materials are capable of exhibiting spectacular wavelength shifts of the order of 600% under the action of an external stimulus. In a particular embodiment of the invention, the dimension of the electromagnetic radiation of at least one of the portions changes relative to another portion such that one wavelength of diffracted electromagnetic radiation is modified by at least 10 nmr at least 25 nm, at least 50 nm, at least 150 nm, at least 2 00 nm, or at least 250 run under the influence of an altering stimulus (i.e. swelling agent}. The photonic materials of the invention may also produce changes in the wavelength of the diffracted electromagnetic radiation of at least 50%, at least 25% or at least 10%. As an example, a photonic material of the invention may diffract electromagnetic radiation of more than 700 nm (infrared, microwave) , when in the presence of an altering stimulus, the dimension of -he electromagnetic radiation of at least one of the portions may change relative no the other portion such that one wavelength of electromagnetic radiation diffracted by the photonic material is modified by at least 1%, 5%, 10%, 25% cr more. The percentage change in said diffracted wavelength may be calculated using the following equation: [ Ui -A0) /A0j X 100 in which Ao corresponds to the peak of the diffracted wavelength before contact with, or in the absence of, an altering stimulus, and A3. corresponds to the peak of the wavelength diffracted during contact with the altering stimulus. Photonic materials in accordance with the invention are described in application US 2009/0086208 and they are prepared using the methods indicated in that document. Photonic material films and particles, in particular having a__polymeric multilayer__interference structure In the context of" the invention, the terms "photonic naterials" and in particular the "polymeric multilayer interference structures" encompass films and particles of photonic materials, in particular having a polymeric multilayer interference structure. In the context of the invention, particles of photonic material, in particular particles having a polymeric multilayer interference structure, may be present within a cosmetic composition. The weight content, relative to the total composition weight, of the particles of photonic material, in particular particles having a polymeric multilayer interference structure, may be in the range 0.1% to 50%, for example in the range 1% to 20%, for example in the range 5% to 15%. It is also possible to use photonic material films, in particular films having a polymeric multilayer interference structure, said films possibly being applied to keratinous materials as well as to materials such as those mentioned above. Said films may be deposited locally on a portion of the external surface of the keratinous materials, for example for protection from solar UV radiation, or to lighten the complexion or for making up, for example to even out the complexion. Sa^ci films may be cut into any format and may, for example, be used to conceal skin imperfections: spots, wrinkles, vitiligo, etc The films of the invention may optionally be adhesive. The films may be adhesive, for example when intended for application to keratinous materials, for example the skin. The films of the invention may be formed in situ on the keratinous materials. Size and form of the polymeric multilayer interference Structures Figure 1 shows a particle having a polymeric multilayer interference structure according to the invention. In the absence or in the presence of a swelling agent, the length Li and the width r..2 of the particle may- be in the range 1 pm to 100 pi. The thickness L3 of particle iTiay be in the range 0.1 µm to 50 µm in the absence of a swelling agent, and in the range 0,1 p to 100 µm in the presence of a swe11i ng agen t. in the absence or in the presence of a swelling agent, the particles having a polymeric multilayer interference structure may have a largest dimension of 100 urn or less- In the absence of a swelling agent, -he pax'ticles may have a largest dimension of 100 µm or less, for example 7 5 urn or less, for example 50 µm or less. In the absence or in the presence of a swelling agent, the particles having a polymeric multilayer interference structure may have a smallest dimension cf 0.1 µm or more, for example 1 pa or more. The film having a polymeric multilayer interference structure iray have a largest dimension in the range 1 irt. to 5 0 cm. The polymeric multilayer interference structures may have a form factor in the range 1 to 1000. The term "form factor" means the ratio of the largest dimension of the polymeric multilayer interference structure to its smallest dimension. The polymeric multilayer interference structures may be plate-like, i.e. have a form factor at least equal to 3, for example at least equal to 10. The polymeric multilayer interference structures may have a lamellar structure, linked to the presence of an amphophilic polymer, for example. The amphophilic polymer may have a lamellar structure. The polymeric multilayer interference structures may comprise at least three layers, for example at least 5, 10 or 50, The polymeric multilayer interference structures may comprise fewer than 100 layers. Method for preparing the polymeric multilayer interference structure As mentioned above, the particles having a polymeric multilayer interference structure may be obtained from a photonic gel, which may be produced as described in the publications by E. Thomas: Nat Ma- Vol 6, 957-960, 2006 and J Am Chem Soc 2009, 131, 7538 - 7539. Figure 2 shows an example of a method of fabricating films and particles having a polymeric multilayer interference structure of the invention. A pho-onic gel is obtained in the form of a film (step i! , for exair.ple by spreading with a film puller, by dip-coating or by spin-coating and by any printing method, for example by ink jet printing a solution of amphophilic block polymer in a solvent. When deposited on a support, it organizes itself spontaneously into a multilayer polymeric structure, for example a lamellar structure. The photonic gel then comprises alternating hydrophiiic and hydrophobic layers. The number of layers of the multilayer structure of the photonic gel nay be 100 or less and its thickness after drying may be 15um or less. After deposition and in the absence of a swelling agent, the photonic gel need not have an interference property in the wavelength range 250 ran to 800 nm. The photonic gel may be quaternized, for example by contact with 1-broruoethane, as described in the publication Nat Mat Vol 6, 957-960, 2008. Contact with a swelling agent (step III) , of nature that is given in detail below, may cause the photonic gel to swell, for example in. its hydrophilic or hydrophobic layers, and thus produce a polymeric multilayer interference structure. As is detailed below, ~he step of contact with the swelling agent may be used advantageously in order to introduce one or more UV screens and/or one or more fluorescent agents and/or one or more coloring agents into the polymeric multilayer structure. The interference wavelength may vary as a function of the concentration, the difference in refractive index between the various layers, the pH of the swelling agent, the molecular weight and the degree of cross-linking cf the polymers present in the polymeric multilayer interference structure. By varying these parameters, it is possible, for example, to cover the whole UVA or UVB spectrum. In Figures 3 and 4, for the purposes of clarity, the relative proportions of the various elements shown have not necessarily been maintained. Figure 3 diagrammatically and partially shows a photonic gel 1 deposited on a support S before contacc with a swelling agent. This photonic gel 1 comprises a polymeric multilayer structure that may, for example and as illustrated, be constituted by alternating hydrophilic 10 and hydrophobic 2 0 lamellar layers. In the embodiment shown "in Figure 3, the photonic gel is transparent to radiation R having, for example, a wavelength in the range 250 mu to 80 0 nm. The term "transparent" means that the photonic gel has no band gap in the wavelength range 450 nm to 8 00 nm. As an example, the photonic gel may have a transmission factor of 80% or more, for example 90% in the wavelength range under consideration. Figure 4 shows the photonic gel 1 of Figure 3 after contact with a swelling agent. In the example of Figure 4, only rhe hydrophobic layers 20 are sensitive to the swelling agent. In a variation, it is possible for only the hydrophilic layers 10 to be sensitive to the swelling agent. As shown, contact with a swelling agent may allow a photonic gel 1 to reflect the radiation R and, for example, provide photoprot-active properties as regards solar UV radiation and/or produce a visible color. The films of the invention may be used once the swelling step has been carried out. A coagulation step (step IV} of coagulating the photonic gel may be carried out after bringing the polymeric multilayer structure into contact with the swelling agent, preferably before or after the fragmentation step. It may comprise bringing the polymeric multilayer structure into contact with a coagulation agent that may be an inorganic material such as silica or its precursors, for example TEOS, or a glycol, for example glycerol, dipropylene glycol, sorbitol, butylene glycol, PEGs having molecular weights in the range 4 00 g/moi to 50000 g/mol. A coagulation step employing a silica precursor, TEOS, in a sol-gel method is described in the publication J Am Cherr. Soc 2G0S, 131, 7533 - 7539. Carrying out a coagulation step may mean that the particles can retain their physico-chemical properties, especially their interference properties, after dispersing them in a cosmetically acceptable medium. The compositions including particles having a polymeric multilayer interference structure comprising a coagulation agent may retain their interfereuce properties during application and for at least 2 hours, for example 3 hours after applying the composition to the keratinous materials. The films having a polymeric multilayer interference structure comprising a coagulation agent may retain their interference properties during application and for at least 2 hours, for example 3 hours after applying the composition to the keratinous materials. Fragmentation step (V) tor fragmenting the polymeric multilayer structure of the photonic gel may be carried out, as illustrated in Figure 2, after the step of making contact with a swelling agenu. and after any step of making contact with a coagulation agent. In a variation, it is possible to carry out the fragmentation step before the step of making contact with a swelling agent, and then to carry out any coagulation step. Fragmentation may, for example, be carried out by laser cutting or milling with an air jet, cryorniiiing, ball milling, or wet milling. Swelling agent In some exemplary embodiments, the photonic material, in particular the polymeric multilayer interference structure, may further include a swelling agent (in particular a non-vclatile swelling agent) in 3 quantity that can swell one or both portions of said material. The swelling agent may, for example, be a mineral oil when the photonic material comprises a polybutadiene / styrene block copolymer in order to swell the polybutadiene portion. Any appropriate solvent may be used as the swelling agent, such as aqueous or organic solvents, for example. In some particular embodiments of the invention, an acidic, neutral, or basic solvent may be used. in the context of the invention, the particles of photonic material, in particular par-ides having a polymeric multilayer interference structure, may include a swelling agent. The swelling agent may be hydrcphilic or hydrophobic depending on the nature of the photonic material portions, in particular the layers of the polymeric multilayer interference structure, which are caused to swell. The swelling agent may include at least one dissolved optically active material, for example a UV screen, a fluorescent agent, a coloring agent and mixtures thereof, The optically active material may, for example, be hydrophobic ox~ hydrophilic. The swelling agent may, for example, comprise a mixture of op-ically active materials, for example a mixture of a UV screen and a fluorescent agent, a mixture of a UV screen and a coloring agent, a mixture of a fluorescent agent and a coloring agent or indeed a mixture of a UV screen, a fluorescent agent and a coloring agent. It is possible to use water as the swelling agent, as well as organic or inorganic saline solutions with a concentration in the range C. 01 M to 5 M, for example solutions of sodium, magnesium, potassium, calcium or copper salts, solutions of phosphates, or ammonium salt solutions. It is also possible to use as the swelling agent, either alone, as a mixture, or in aqueous solution ar.d in any proportions, glycerol, PEGs having a molecular weight in the range 400 g/mel to 50000 g/'mol, mono-, di- and cligo-saccharides thar are soluble in water in a proportion of at least 1% by weight, sorbitol, propylene glycol, diprcpylene glycol, ethylene glycol, butylene glycol, water-soluble polyols, lower alcohols tha: are rtiiscible in water, for example methanol, ethanol or isopropanol, or 1-butanol. The term "lower alcohol" means an alcohol having fewer than 6 carbon atoms- Examples of other suitable solvents that may be mentioned are benzene, acetone, p-methylbutyric acid, oc- ethylbutyric acid, 2,2,2,-trifluoroethanol, 1-butanol, 1,4-butanediol, chloroform, bromoethane, methyl acetate, ethyl acetate, dimethylformamide, butan-2-one, divinylbenzene, propylene glycol monomethylether acetate (PGHSA), and acetic acid solutions. The swelling agent may further comprise or even consist of a UV screen solution, for example organic, neutralized or not neutralized. The following solutions may be mentioned: terephthalylidene dicamphor SULFONIC ACID, lor example Mexoryl SX or PHENYLBEtfZIMIDAZOLE SULFONIC ACID, for example Eusolex 232. Using a solution of non-neutralized organic UV screen(s) would mean that the pH could be varied and thus the swelling of the photonic material, especially the polymeric multilayer structure, for example the amphophilic polymer, can also be varied. The swelling agent may also be selected from polar oils such as lauroyl isopropyl sarcosinate, octyldodecanol, a C12-Ci5 alkylbensoate {Finsolv TN) , imaecane and tridecane, for example, as well as oily solutions of organic screens, for example when the particles of photonic material, in particular particles having a polymeric multilayer interference structure, for example the amphiphilic polymer, comprise at least a portion, in particular a layer, which is hydrophobic and sensitive to the swelling agent. The pH of the swelling agent may be in the range 1 to 12 . it may be modified by contact with acids and bases selected, for example, from acetic, lactic, hydrochloric, nitric, sulfuric, maleic, and succinic acid, and bases such as sodium hydroxide, potassium hydroxide, triethanolamine, or solutiong of lysine and arginine. Fixing agent The particles of photonic material, in particular particles having a polymeric multilayer interference structure, may include a fixing agent. A fixing agent may be selected from inorganic compounds, for example silica and its precursors, for example TEOS, or glycols, for example glycerol, dipropylene glycol, sorbitol, butylene glycol, or PEGs having molecular weights in the range 400 g/mol to 50000 g/mol. The difference in the refractive index of the fixing agent and the layers of the polymeric multilayer interference structure may be in the range 0.05 to 1.5. Polymers of photonic materials and o£ polymeric multilayer interference structures The photonic materials, in particular the polymeric multilayer interference structures, of the invention may include homopolymers, copolymers, block copolymers, mixtures of homopolymers, mixtures of block copolymers, mixtures of homopolymers and block copolymers, polymeric materials associated with additives such as colorants, or inorganic compounds. In some exemplary embodiments, the photonic materials may comprise mixtures of polymers or mixtures of polymers and nor—polymers or others, and may include at least two portions with different compositions and/or having different chemical. physical, or dielectric properties. Furthermore, the photonic materials of the invention may contain other polymeric, or . non-polymeric additives that may be used to modify the dimension, the chemical or the physical properties of at least one of the portions. In addition, a non-polymeric additive present in the structure of the photonic material may constitute a region separating two portions within the periodic structure. As an example, the size of the separated polymeric portions may be controlled by modifying a fraction of the volume of the portion, for example by incorporating auxiliary nanoparticles, auxiliary horaopoiymers, auxiliary monomers, or cross-linkable compounds ~hat are polymerized, grafted, and/or cross- linked in situ. The additives such as those mentioned above nay be used to modify the number/type of the portion and/or the dimensions of the portion but will noi: influence the behavior of rhe photonic material under the influence of an altering stimulus. Block copolymer The block copolymers present in the photonic materials of the invention may result in one-, two- or three-dimensional periodic structures arranged in separate portions characterized by different compositions and/or different physical properties. The term "periodic structure" is used to mean a structure arranged such that a straight line in at least one direction passes through said structure and intersects at least two separate portions at regular' intervals. As an example, a "one-dimensional structure" is a structure that may be oriented in an orthogonal system of coordinates in three dimensions {components in the X, Y, 2 directions) such that a straight line in a single direction passes through said structure and intersects an lease two separated portions at regular integrals. A "twc-dimsnsional structure" is a structure that may be oriented in a 3-dimensional coordinate system such that straight lines in. two directions pass through- said structure and intersect at least two separate portions at regular intervals. A "three-dimensional structure" is a structure that may be orier.ted in a 3- dimensional coordinate system such that a straight liny in any of the three directions passes through said structure and intersects at least two separate portions at regular intervals. In addition, the term "periodic structure" refers to a material with portions having a regular periodicity characterized ay similar portions having similar dimensions and spacings in the photonic material. The term "portion" defines a distinct region of the photonic material characterized by a particular composition and/or particular physical properries that distinguish it from those of adjacent or surrounding portions. The polymer constituting the photonic material, in particular the polymeric multilayer interference structure, may bo amphiphilic and may comprise or, for example, may be a block copolymer, for example a: - diblock copolymer with the form A-B where A is a hydrophobic block selected, for example, from; polystyrene, polymethyl methacrylate, polycyclohexyi methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide, and polyisoprcpyi methacrylate, and B is a: • hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4-vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolidone); • hydrophilic and anionic block, for example selected from: poly(acrylic acid), poly(methacrylic acid), poiyfmaleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2-methylpropane sulfonic acid] ,• or • hydrophilic and ncn-ionic block, for example selected from: poly(PEG methacrylate); - triblock copolymer with the form A-B-C where: • A and C are different hydrophobic blocks, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylandde, and polyisopropyl methacrylate, and B is a: c hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly{4-vinyl pyridine), poly(dimethyl amino ethyl methacrylate}, poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly, Neocryl A-1070®, Neocryl A-109G®, Neocryl 3T-62®, Neocryl A-107 9® and Neocryl A-523® by the supplier AVECIA- NEORESINS, Dow Latex 432® by the supplier DOW CHEMICAL, Daitosol 5000 AD© or Daitosol 5000 SJ® by the supplier DAITO KASSY KOGYO, Syntran 5760® by the supplier interpoiymer, Allianz OPT by the supplier ROHM & HAAS, aqueous dispersions of acrylic or styrene/acrylic polymers sold under the trade name JONCRYL® by the supplier JOHNSON POLYMER, or aqueous dispersions of polyurethane sold under the names Neorez R-981® and Neorez R-974® by the supplier AVECIA-NSQRESINS, Avalure UR-4C5®, Avalure UR-410®, Avalure UR-425®, Avalure UR-450®, Sancure 375®, Sancure 861©, Sancure 878® and sancure 206 0® by the supplier GOODRICH, Impranil 85® by the supplier BAYER, Aquamere H-1511® by the supplier HYDROMER, sul£opolyesters sold under the trade name Eastman AQ® by the supplier Eastman Chemical Products, vinyl dispersions such as Mexomere PAM® from the supplier CHIMEX and mixtures thereof. The term "amphophilic or associative polymers" means polymers comprising one or more hydrophilic portions that render then partially soluble in water and one or more hydrophobic portions via which the polymers associate or interact. The following associative polymers may be used: Nuvis FX1100® from Elementis, Aculyn 22®, Aculyn 44®, Aculyn 46® from Rohm&Haas, and Viscophobe DB1Q00® from AMERCHOL. Diblock copolymers constituted by a hydrophilic block (polyacrylate, polyethylene glycol) and a hydrophobic block (polystyrene, polysiloxane) may also be used. The composition may comprise an oily phase and the film-forming polymer may be present in said oily phase. The polymer may then be in dispersion or in solution. NAD type polymers or microgels (for example KSGs) nay be used, as well as polymers of the PS-PA type or copolymers based on styrene (Kratoa, Regalite). Examples of non-aqueous dispersions of polymer particles in one or more silicone and/or hydrocarbon oils that can be stabilized at their surface by at least one stabilizing agent, in particular a block, graft or random polymer, that may be mentioned are acrylic dispersions in isododecane, such as Mexcmere PAP® from the supplier CHIMEX, and dispersions of particles of a graft ethylenic polymer, preferably acrylic, in a liquid fatty phase, the ethylenic polymer advantageously being dispersed in the absence of an additional particle surface stabilizer such as that described in particular in the document WO 04/055081. Film-forming polymers that may be used in the composition of the present invention that may be mentioned are synthetic polymers of the radical or polycondensation type, polymers of natural origin, and mixtures thereof. In particular, the radical type film-forming polymers may be polymers or copolymers, which are vinyls, especially acrylic polymers. Vinyl film-forming polymers may result from polymerizing monomers containing an etliylenically unsaturated bond having at least one acid group and/or esters of said acid monomers and/or amides of said acid monomers, such as unsaturated a,p-ethylenically unsaturated carboxylic acids, for example acrylic acid, methacrylic acid, crotonic acid, maleic acid or itaconic acid. Polymers of natural origin, optionally modified, may be selected from shellac resin, sandarac gum, dammars, elemis, copals, and cellulose polymers such as nitrocellulose, ethylcelluiose or nitrocellulose esters selected, for example, from cellulose acetate, cellulose acetobutyrate, cellulose acetopropionate, and mixtures thereof. The film-forming polymer may be present in the form of solid particles in aqueous or oily dispersion, generally known as a latex or pseudclatex. The film- forming polymer may comprise one or more suable dispersions of particles of generally spherical polymers of one or more polymers, in a physiologically acceptable, liquid fatty phase. These dispersions are generally termed polymer NADs, as opposed to latexes that are aqueous polymer dispersions. These dispersions may in particular be in the form of nanoparticles of polymers in stable dispersion in said fatty phase. The nanoparticle size is preferably in the range 5 ran to 600 nm. The techniques for preparing said dispersions are well known to the skilled person. The composition may comprise at least one film- forming polymer that is a linear block ethylenic film- forming polymer. Said polymer may comprise at least one first sequence {block} and at least one second sequence having different glass transition temperatures (Tg), said first and second sequences being connected together via an intermediate sequence comprising at least one constitutive monomer of the first sequence and at least one constitutive monomer of the second sequence. As an example, the first and second sequences and the block polymer are incompatible with each other. Such polymers, for example, are described in the documents EP 1 411 069 or WO 04/028483, which are herewith incorporated by- reference. Aqueous phase The compositions of the invention may include at least one aqueous phase. The compositions of the invention, may include an aqueous phase that may include particles of photonic material, in particular particles having a polymeric multilayer interference structure. The water content of the aqueous phase is, for example, greater than or equal to 30% by weight, more preferably 40% by weight, highly preferably 50% by weight. The aqueous phase may also include a mixture of water and (an) organic solvent (s) raiseible with wa:er {miscibility in water greater than 50% by weight at 25°C) such as lower monoalcohols containing 1 to 5 carbon atoms such as ethanol, isopropanol, glycols containing 2 to 8 carbon atoms such, as propylene glycol, ethylene glycol, 1,3-butylene glycol, dipropylene glycol, C3-C1 ketones, and C2-C4 aldehydes. The aqueous phase may be present in an amount in the range 1% to 99% by weight, in particular in the range 3% to 80% by weight, and more particularly in the range 5% to 60% by weight relative to the total weight of the composition under consideration. Fatty Phase In all of the embodiments under consideration, the compositions of the invention may include a fatty phase. The fatty phase may, for example, be free of particles of photonic material, in particular particles having a polymeric multilayer interference structure. The composition may comprise an oil such as, for example, synthesized esters or ethers, linear or branched hydrocarbons of mineral or synthetic origin, fatty alcohols containing 8 to 26 carbon atoms, partially fluorinated hydrocarbon and/or silicone oils, silicone oils such as polymethylsiloxanes (PDMS) , which may optionally be volatile, with a linear or cyclic silicone chain, which may be liquid or pasty at ambient -ernperature, and mixtures thereof; other examples are given bslow. A composition in accordance with the invention may thus comprise at least one volatile oil. Volatile oils In the context of the present invention, the term "volatile oil" means an oil (or non-aqueous medium} that is capable of evaporating on contact with skin in less than one hour, at ambient temperature and at atmospheric pressure. The volatile oil is a volatile cosmetic oil, liquit at. ambient temperature, in particular having a r.on-zen vapor pressure, at ambient temperature and atmospheric pressure, in particular having a vapor pressure in th< range 0.13 Pa to 40000 Pa (10~3mmHg to 300 iraiHg), i] particular in the range 1.3 Pa to 13C00 Pa (0.01 mnHg t( 100 mmHg) , and more particularly in the range 1.3 Pa t< 1300 Pa (0.01 mmHg to 10 mmHg) . The volatile hydrocarbon oils may be selected froi hydrocarbon oils of animal or vegetable origin containing 8 to 16 carbon atoms, and in particular branched Ce-Ca elkanes (also termed isoparaffins) , such as isododecan. (also termed 2,2,4,4,6-pentamethylheptane), isodecane isohexadecane and, for example, oils sold under the trad* names isopars® or Permethyis®. Examples of volatile oils that may also be used ar< volatile silicones, for example linear or cyclic volatile silicone oils, especially those with a viscosity of 10. The esters may he in particular be selected frorr. esters, in particular of fatty acids, such as, for example: • cetostearyl octanoate, esiers of isopropyl alcohol such as isopropyl myristate, isopropyl palmitate, ethyl palmitate, 2-ethylhexyl palmitate, isopropyl stearate or isostearate, isostearyl isostearate, octyl stearate, hydroxy1 esters such as isostearyl lactate, octyl hydroxystearate, diisopropyl adipate, heptanoates, in particular isostearyl heptanoate, octanoates, decanoates or ricinoleates of alcohols or polyalcohols, such as propylene glycol dioctanoate, cetyl octanoate, tridecyl octanoate, 2-ethylhexyl 4-diheptanoate and palmitate, alkyl benzoate, polyethylene glycol diheptanoate, propylene glycol 2-diethyl hexanoa~e and mixtures thereof, Ci2-c:5 alcohol benzoates, hexyl laurate, neopentanoic acid esters such as isodecyl neopentanoaue, isotridecyl neopentanoate, isostearyl neopentanoaze, octyldodecyl neopentanoate, isononanoic acid esters such as isononyl isononanoate, isotridecyl isononanoate, octyl isononanoate, or hydroxyl esters such as isostearyl lactate, or di-isosr.earyl malate; • esters of polyols, and penraetrythritol esters, such as diper.taerythritol cetrahydroxystearate / tetraisos tearate; • esters of diol dimers and diacid dimers, such as Lusplan DD-DA5® and Lusplan DD-DA7®, sold by the supplier NIPPON FINE CHEMICAL and described in application FR 03 0280S; • fatty alcohols that are liquid at ambient temperature having a branched and/or unsaturated carbon chain containing 3 2 to 26 carbon atoms, such as 2- octyldodecanol, isostearyl alcohol, oleic alcohol, 2- hexyldecanol, 2-butyloctanol, or 2-undecylpentadecanol; • higher fatty acids such as oleic acid, linoleic acid, linolenic acid and mixtures thereof; and • dialkyl carbonates, the 2 alkyl chains possibly being identical or different, such as dicaprylyl carbonate sold under the name Cetiol CC®, by Cognis; • non-volatile silicone oils such as, for example, non-volatile polydimethylsiloxanes (PDMS), polydimethylsiloxanes comprising pendant alkyl cr alkoxy groups and/or with silicone chain ends, the groups each containing 2 to 24 carbon atoms r phenyl silicones such as phenyl trimethicones, phenyl dimethicones, phenyl trimethylsiloxy dipiienylsiloxan.es, diphenyl dimethicones, diphenyl methyldiphenyl trisiloxanes, or 2~phenylethy± trimethylsiloxysilicates, or dimethicones or phenyl^rirr.ethicone with a viscosity less than or equal to 10G cSt, and mixtures thereof,- - and mixtures thereof. Surfactants The composition of the invention may further contain emulsifying and co-emulsifying surfactants present, for example, in a proportion in the range 0.1% to 30% by weigh- relative to the total composition weight. Said surfactants may be selected from anionic or non-ionic surfactants. Reference should be made to the document "The Encyclopedia of Chemical Technology, KIRK- OTHKER, volume 22, pp 333 - 432, third edition, 1979, WILZY, for a definition of the properties and functions of the surfactants, in particular pp 347 - 377 of said reference, for the anionic and non-ionic surfactants. Examples of surfactants that may be employed in the invention and are suitable for producing a W/0 emulsion that may be mentioned are dimethicone copolyols such as the mixture of cyclomethicone and dimethicone copolyol sold under the name DC 522 b C by the supplier Dow corning, and dimethicone copolyols such as laurylmethicone copolyol sold, under the name Dow Corning 520 0 Formulation Aid by the supplier Dow Corning and cetyl dimethicone copolyol sold under the name ABIL EH 90R by the supplier GOLDSCKMIDT, or the polygiyceryl-4 isostearate / cetyl dimethicone copolyol / hexyllaurate mixture sold under the name ABIL WE 09 by the supplier GOLDSCHMIDT. In is possible to add thereto one or more co- emulsifying agents that may, for example, be selected from the group comprising alkylated polyol esters. Particular examples of alkylated polyol esters that may be mentioned are esters of glycerol and/or sorbitan, for example polyglycerol isostearate, such as the composition sold under the name isolan GI 34 by the supplier GOLDSCHMIDT, sorbitan isostearate, such as the composition sold under the name ARLACEL- 9 87 by the supplier ICI, sorbitan and glycerol isostearate, such as the composition sold under the name ARLACEL 9 86 by the supplier ici, and mixtures thereof. Polyisobutylene surfactants containing esterified succinic end groups, such as those sold under the names Lubrizol 5603 and Chemcinnate 2 00C hy the suppliers Lubrizol and Cheirror., may also be used as emulsifiers suitable for obtaining a W/0 emulsion. Surfactants for w/0 emulsions that may also be used include a solid cross-linked elastomeric organopoiysiloxane comprising a~ least one oxyalkylene group, such as those obtained according to the procedure of Examples 3, 4 and S of document: US-A-5 412 004 and cf the examples of document US-A-5 611 487, especially the product of Example 3 (synthesis example) of patent US-A-5 412 004, and such as the product sold under the reference KSG 21 by the supplier Shin-Etsu. Examples of surfactants that may be used in the invention that are suitable for obtaining an O/W emulsion that may be mentioned are non-ionic surfactants, and especially esters of polyols and of fatty acids with a saturated or unsaturated chain containing, for example, 8 to 24 carbon atoms and more preferably 12 to 22 carbon atoms, and their oxyalkylenated derivatives, i.e. derivatives containing oxyethylenated and/or oxypropylenatad units, such as the glyceryl esters of Cg- C24 fatty acids, and their oxyalkylenated derivatives; polyethylene glycol esters of C8-C24 fatty acids, and their oxyalkylenated derivatives; sorbitol esters of Cg- C2i fatty acids, and their oxyalkylenated derivatives; sugar (sucrose, glucose or alkylglucose) esters of Cs-C2i fatty acids, and their oxyalkylenated derivatives; ethers of fatty alcohols; sugar ethers of C8-C24 fatty alcohols; oxyethylenated fatty acid ethers of glucose or alkylglucose; and mixtures thereof. Glyceryl esters of fatty acids that may in particular be mentioned include glyceryl stearate (glyceryl mono-, di- and/or tristearate) (CTFA name: glyceryl stearate) or glyceryl ricinoleate, and mixtures thereof. Polyethylene glycol esters of fatty acids that may in particular be mentioned include polyethylene glycol stearate (polyethylene glycol mono-, di- and/or tristearate) and more especially polyethylene glycol 50 OH monosteara-e (CTFA name: PEG-50 stearate), polyethylene glycol 100 oe monostearate [CTFA name: FEG-100 stearate) and mixtures thereof. It is also possible to use mixtures of these surfactants, such as the product containing glyceryl stearate and PEG-100 stearate, sold under the name ARLACEL 155 by the supplier Uniqema, and the product containing glyceryl stearate (glyceryl mono-d.istearate) and potassium stearate, sold under the name TEGIN by the supplier GCLDSCHMIDT (CTFA name: glyceryl stearate SE). Fatty acid esters of glucose or of alkylglucose that may in particular be mentioned include glucose palmitate, alkylglucose sesquistearates, such as methyl glucose sesquistearate, alkylglucose palmitates, such as methylglucose or ethylglucose palmitate, fatty esters of methylglucoside and more especially the diester of methylglucoside and of oleic acid (CTFA name: Methyl glucose dioleate) ,- the mixed ester of methylglucoside and of the oleic acid / hydroxystearic acid mixture (CTFA name: Methyl glucose dioleate / hydroxystearate); the ester of methylglucoside and isostearic acid (CTFA name: Methyl glucose isostearate); the ester of methylglucoside and lauric acid (CTFA name: Methyl glucose laurate); the mixture of the monoester and diester of methylglucoside and isostearic acid (CTFA name: Methyl glucose sesqui- isostearate); the mixture of the monoester and diester of methylglucoside and stearic acid {CTFA name: Methyl glucose sesquistearate) and in particular the product sold under the name Glucate SS by the supplier AMERCHOL, and mixtures thereof. Examples of oxyethylenated ethers of a fatty acid and glucose or alkylglucose that may be mentioned include the oxyethylenated ethers of a fatty acid and methylglucose, for example the polyethylene glycol ether of the diester cf methyl glucose and stearic acid containing approximately 20 moi of ethylene oxide (CTFA name: PBG-20 methyl glucose distearate), such as the product sold under ~he name Giucam E-2 0 distearate by the supplier AKERCHOL; the polyethylene glycol ether of the mixture of the monoester and diester cf mezhylgiucose and stearic acid containing about 2 0 moi of ethylene oxide (CTFA name: PEG-2C methyl glucose sesquistearate}, for example the produce sold under the name Giucamate SSE-2 0 by the supplier AMERCHOL, and the product sold, under the name Grillccose PSE-20 by the supplier GOLDSCKMIDT, and mixtures thereof. Examples of sucrose esters that may be mentioned include saccharose palmitostearate, saccharose stearate and saccharose monolaurate. Examples of ethers of fatty alcohols that may be mentioned include polyethylene glycol ethers of fatty alcohols containing 8 to 30 carbon atoms and especially 10 to 22 carbon atoms, such as polyethylene glycol ethers of cetyl alcohol, stearyl alcohol or cetearyl alcohol {mixture of cetyl and stearyl alcohol). Examples that may be mentioned include ethers comprising 1 to 2 00 and preferably 2 to 100 oxyethylene groups, such as those with CTFA name Ceteareth-2C and Ceteareth-30, and mixtures thereof. Sugar ethers that may in particular be mentioned are alkyIpolyglucosides, for example decylglucoside, such as the product sold under the name MYDQL 10 by the supplier Kao Chemicals, the product sold under the name PLAWTAREN 2 000 by the supplier Henkel, and the product sold under the name ORAMIX HS 10 by the supplier SEPPIC; caprylyl / capryl glucoside, such as the product sold under the name ORAMIX CG 110 by the supplier SEPPIC or under the name L'JTEMSOL GD 70 by the supplier BASF; laurylglucoside, such as the products sold under the names PLANTAREN 1200 W and PLANTACARE 1200 by the supplier Henkel; cocoglucoside, such as the product sold under the name PLANTACARE 818/UP by the supplier Henkel; cetostearyl glucoside optionally as a mixture with cetostearyl alcohol, sold, for example, under the name MONTANOV 68 by the supplier SEPPIC, under the name TEGO-CARE CG90 by the supplier GOLDSCHMIDT and under the name EMULGADE KE3302 by the supplier Henkel; arachidyl glucoside, for example in the form of the mixture of arachidyl alcohol and behenyl alcohol and arachidyl glucoside, sold "under the name MONTANOV 202 by the supplier SEPPIC; cocoylethylglucoside, for example in the form of a mixture (35/65) with cetyl and stearyl alcohol, sold under the name MOKTTANOV 82 by the supplier SSPPIC, and mixtures thereof. The composition according to the invention may also contain amphiphilic polymers as enuzlsifiers or co- emulsifiers. The term "amphiphilic polymer" means any polymer comprising both a hydrophilic portion and a hydrophobic portion separating two liquids of different polarity and thus allowing liquid-liquid dispersions of a direct, inverse or multiple type to be stabilized. The amphiphilic polymer may reduce the water/oil interfacial tension to 10 mN/rn, irrespective of the oil. These polymers are ionic (anionic or cationic) or amphoteric. The amphiphilic polymers in accordance with the invention generally have a number average molecular weight in the range 1000 g/mol to 20000000 g/mol, preferably in the range 20000 to 8000000, for example in the range 100000 g/mol to 700000 g/mol. The quantity of amphiphilic polymer used in accordance with the invention may be in the range 0.01% to 20% by weight, preferably 0.1% to 10% by weight, for example 0.2% to 5% by weight. Particular examples that may be used are acrylate / C10-C3Q- alkylacrylate copolymers such as the products sold under the names PEMULEN TRl, PEMULEN TR2 and CARBOPOL 1382 by the supplier GOODRICH, or mixtures thereof. it is also possible to use acrylate / steareth-20 itaconate copolymers and acrylate / ceteth-2 0 itaconate copolymers sold under the names STRUCTURE 20C1 and STRUCTURE 3001 by the supplier NATIONAL STARCH. Particularly suitable cross-linked or non cross-linked amphiphilic polymers are the products sold under the names ARISTOFLBX LNC, ARISTOFLEX SKC, and ARISTOFLEX EMS by the supplier CLARIANT. An example of a terpolymer that may be mentioned is the methacrylic acid / methyl acrylate / behenyl dimethyl-m- isopropenylbenzylisocyanate terpolymer ethoxylated with 40 EO units, sold by the supplier AMERCHOL under the names VISCOPHOBE DB 1000 NP3-NP4. It is also possible to mention cross-linked terpoiymers of methacrylic acid, ethyl aerylate, polyethylene glycol stearyl ether (10 EO) (Steareth 10) , such as those sold by the supplier allied Colloids under the name SALCARE SC 80. Examples of anionic polymers for use in the invention are polymers of i soph thai ic acid or sulfoisophthalic acid, in particular copolymers of phthalate / sulfoisophthalate / glycol (for example diethylene glycol / phthalate / isophthalate / 1,4- cyclohexanediitiethanol) sold under the name "Eastman AQ Polymer" (AQ 35S, AQ 38S, AQ 55S and AQ 48 Ultra) by the supplier Eastman Chemical. Additives The composition comprising the particles of photonic material, in particular particles having a polymeric multilayer interference structure, may comprise at least one additive selected from adjuvants that are normal in the cosmetics field, such as fillers, softening agents, coloring agents, surfactants, hydrophilic or lipophilic gelling agents, active ingredients, either hydrosoluble or liposoluble, preservatives, moisturizers such as polyols and in particular glycerin, sequestrating agents, antioxidants, solvents, fragrances, physical and chemical sunscreens, especially against TJVA and/or UVB, odor absorbers, pH adjusting agents (acids or bases), and mixtures thereof. The composition may contain at least one active ingredient having a complementary activity in the solar protection field, such as antioxidants, whitening agents in the context of anti-pigmentation and depigmentation, or anti-ageing active ingredients. The additive or additives may be selected from those cited in the CTFA Cosmetic Ingredient Handbook, 10th Edition, Cosmetic and Fragrance Assn., inc, Washington DC (2004), herev?ith incorporated by reference. Galenical dosage forms The particles of photonic material, in particular particles having a polymeric multilayer interference structure, may be used in lotions, creams, milks, balms, pommades, gels, emulsions, films, patches, sticks, for example lipsticks, powders, or pastes, for the skin, the lips, the hair or the nails. The particles of the invention may, for example, be incorporated into any type of cosmetic composition, for example of the gloes, lipstick, eye-liner, mascara, foundation, eyeshadow, nail polish etc type. The photonic material films, in particular films having a polymeric multilayer interference structure of the invention, may bs applied by transfer. Before application to the keratinous materials, said films may be attached to an adhesive layer. When the cosmetic composition of the invention is used to protect the hair against solar UV radiation, it may be in the form of a shampoo, lotion, gel, emulsion, or non-ionic vesicular dispersion, and may, for example, constitute a rinse-out composition, a composition for application before or after shampooing, before or after coloring or stripping, before, during or after penning or straightening, as a setting or treatment lotion, a lotion or gel for blow drying or setting, a perming or straightening composition, or for coloring or stripping the hair. Modes of application The composition including parricles of photonic material, in particular particles having a polymeric multilayer interference structure, may be applied, with the hand or using an applicator. Application may also be accomplished by spraying or projection using a piezoelectric device, for example, or by transfer of a layer of composition that has been deposited on an intermediate support. Packaging The composition may toe packaged in any packaging device, especially formed from thermoplastic material, or on any support provided for that purpose. The packaging device may be a bottle, a pump bottle, an aerosol bottle, a tube, a sachet, or a pot. Examples Example 1 A gel of polystyrene-poly<2-vinylpyridine) quaternised diblock copolymer (PS-D-Q-P2VP) (190K/19QK) with a thickness of 3 urn (dry) was obtained by dip coating, on a rigid surface, from a 5% by weight PS-b-Q- P2VP solution in propylene glycol monomethyl ether acetate. The gel was then swollen using an agueous 2.5 M NH4CI solution. A photonic gel interfering in the wavelength range 340 ran to 385 nir. was obtained. This photonic gel film was suitable for use as a photoprotective agent for keratinous materials. Example 2 The gel from Example 1 was detached from the rigid support then fragmented before swelling into particles with a largest dimension of less than 50 uir. using a dry bail mill. The particles thus obtained were then dispersed in an aqueous 2.5 M NHjCI solution. After separating by filtration, particles having a polymeric multilayer interference structure interfering ir. the TJV range (between 340 nm and 385 rim) were obtained. Example 3 A 3 pm thick (dry) ?S-b-Q-P2VP (190K/19CK) gel was spread over a rigid support then fragmented before gwelling into particles with a largest dimension of less than 5C urn using a dry ball mill. The particles thus obtained were then dispersed in a mixture containing 50% by weight of glycerol and 50% by weight of an aqueous 2.5 M NH4Cl solution. After separating, particles having a polymeric multilayer interference structure interfering in the wavelength range 340 nm to 385 nm were obtained. Introducing glycerol had the effect of preserving the interference properties of the photonic gel after drying. Example 4: Photoprotective cosmetic composition based on photonic gel particles Fatty phase ARISTOFLEX LNC {CLARIANT) 1% Cyclopentasiloxane 6% Oc-ylpaliaitate 6% Aqueous phase Particles of phoconic gel produced in Example 3 10% Glycerol 5% Preservative 0.3% Water qsp 100% Example 5: Production of photonic gel particles coagulated with silica A 3 µm thick (dry) PS-b-Q~F2VP (190K/19DK) gel was obtained by dip coating, on a rigid surface, from a 5% P£-b-Q-?2v? solution in propylene glycol monomethyl ether acetate. The gel was then fragmented, before swelling into particles with a largest dimension of less than 50 µm using a dry ball mill. The particles obtained were then dispersed and swollen in methanol. An aqueous solution of TEOS (tetraethoxysilane) with a concentration 0.45 M was then added. An aqueous 2.5 M WHaCl solution was added with vigorous stirring. Particles having a polymeric multilayer interference structure interfering in the wavelength range 340 nm to 385 nm and insensitive to the dispersion medium were obtained. Example 6: Photonic gel swollen with an aqueous sunscreen solution A 3 µm thick (dry) PS-D-Q-P2VP (19OK/19OK) gel was obtained by dip coating, on a rigid surface, from a 5% PS-b-Q-P2VP solution in propylene glycol monomethyl ether acetate. This gel was then swollen with an aqueous 3% solution of Mexcryl SX (Chimex) (TEREPHTHALYLIDENE DICAMPHOR SULFONIC ACID, 33% in water), A phoconic gel interfering in the wavelength range 33 0 nm to 3B5 nm with a significantly reduced goniochroinatic effect was thus obtained. Said photonic gel film was suitable for use as a phoroprotective agent for keratinous materials. Example 7: Photonic gel swollen with an aqueous sunscreen solution A 3 µm thick (dry) PS-b-Q-?2VF (190K/190K) gel was obtained by dip coating, on a rigid surface, from a 5% PS-b-Q-P2VP solution ir. propylene glycol monomethyl ether acetate. This gel was swollen with an aqueous D.5% solution of 2usolex 232 (Merck) (PHENYLBEKZIMIDAZCLE SULFONIC ACID). A photonic gel interfering in the wavelength range 230 nm to 385 nm was thus obtained. Said photonic gel film was suitable for use as a photoprotective agent for keratinous materials. Example 3:____Photoprotective____cosmetic composition comprising two types of particles with polymeric multilayer interference structures that interfere differently and in a complementary manner with UV Fatty phase ARISTOFLEX LATC (CLARIANT) 1% Cyclopentasiloxane 6% Octylpalmitate 6% Aqueous phase Particles having a polymeric multilayer interference structure obtained by ball milling a photonic gel from Example 6 5% Particles having a polymeric multilayer interference structure obtained by ball milling a photonic gel from Example 7 5% Glycerol 5% Preservative 0.3% Water qsp 100% Example 9.-____Fhotoprotective cosmetic composition comprising two types of particles with polymeric multilayer interference structures that interfere -differently and in a complementary manner with UV Fatty phase ARISTOFLEX LNC (CLARIANT) 1% Cyclopentasiloxane 6% Octylpalmitate 6% Aqueous phase Particles having a polymeric multilayer interference structure from Example 2 5% Particles having a polymeric rmilnilayer interference structure similar to those of Example 1 but swollen with a 1 M solution of NH4CI obtained, using the method of Example 2 5% Glycerol 5% Preservative 0.3% Water qsp 100% Example 10: Photonic gel swollen with an optical brightener solution A 3 urn thick (dry) PS-b-Q-P2vp (190K/190K) gel was obtained by dip coating, on a rigid surface, from a 5% PS-b-Q-P2v? solution in propylene glycol monomethyl ether acetate. Said gel was then swollen with an aqueous 0.5% solution of Tinopal CBS X (CIBA) (MSODIUK DISTYK.YLBI PHENYL DlSULFONATE). A photonic gel interfering in the UV region and colored blue 'was obtained that was suitable, once fragmented, for use in lightening human kerarinous materials, for example the skin. Example 11: Colored photonic gel A 3 urn thick (dry) PS-b-Q-P2VP (190K/190K) gel was obtained by dip coating, on a rigid surface, from a 5% ?S-b-Q-P2VP solution in propylene glycol monomethyl ether acetate. Said gel was then swollen with an aqueous 1.5 M NH4CI solution. The reflected wavelength corresponding to the transmission minimum was approximately 550 mi, i.e. a yellow color. The film was suitable, for example, for use to even out the complexion either before or after fragmentation. Example 12: Colored photonic gel A 3 mm thick (dry) ?S-b-Q-?2VP {19CK/190K) gel was obtained by dip coating, on a rigid surface, from a 5% PS-b-Q~P2VP solution in propylene glycol rncnomethyl ether acetate. Said gel was swollen with an aqueous 0.5 M NE^Cl solution. The reflected wavelength corresponding to the transmission minimum was approximately 410-420 nm, i.e. a violet color. The film was suitable, for example, for use to even out the complexion either before or after fragmentation. example 13: Colored photonic gel A 3 µm thick (dry) PS-b-Q-P2VP (19 0K/190K) gel was obtained by dip coating, on a rigid surface, from a 5% PS-b-Q-P2VP solution in propylene glycol monomethy]. ether acetate. Said gel was then swollen with an aqueous 1 M NH4Cl solution. The reflected wavelength corresponding ,to the transmission minimum was approximately 600 nm, i.e. a yellow-orange color. The film was suitable, for example, for use to even out the complexion either before or after fragmentation. The photonic gels described in Examples 11 to 13 could be fragmented using the method of Example 2. The photonic gels described above, for example the colored photonic gels of Examples 11 to 13, could be coagulated by the action of a silica precursor (TEOS) or with glycerol, as in Example 3. Example 14: Reflection spectrum of a photonic gel Figure 5 shows two absorption spectra of a PS-P2VP photonic gel from the publication Wat Mat. Vol 6, 957-960, 2008. The absorption peaks measured correspond to the transmission minima and to the reflection peaks of the photonic gel. In the absence of a swelling agent, the absorption spectrum had no peak and the photonic gel did not have interference properties. in contrast, when the photonic gel was swollen with pure water, the absorption spectrum could, as shown, have 5 reflection bands each corresponding to a distinct order of interference. The peak in the UV in this example corresponds to an order of interference of 5. Unless otherwise specified, the expression "comprising a" should be construed as meaning "comprising at least one". CLAIMS 1. A photoprotective cosmetic composition including particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer. 2. A composition according to claim 1, wherein the particles having a polymeric multilayer interference structure have a reflection spectrum including a reflection peak in the wavelength range 2 50 nm to 400 nm. 3. A composition according to claim 1 or 2, wherein the amphiphilic polymer includes a swelling agent. 4. A composition according to any preceding claim, comprising a fatty phase and an agueous phase, the aqueous phase including particles having a polymeric multilayer interference structure. 5. A composition according to any preceding claim, wherein the particles having a polymeric multilayer interference structure include a fixing agent selected from inorganic materials, for example silica and its precursors for example TEOS, glycols, for example glycerol, dipropylene glycol, sorbitol, butylene glycol, and PEGs having a molecular weight in the range 400 g/mol to 50000 g/mol. 6. A composition according to any preceding claim, including at least two different types of particles having a polymeric multilayer interference structure, each particle type having a different transmission spectrum in the wavelength range 250 nm to 400 nm. 7. A composition according to any preceding claim, wherein the amphophilic polymer has a lamellar structure. 8. A composition according to any preceding claim, wherein the amphiphilic polymer comprises a block copolymer. 9. A composition according to the preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, a: - dibiock copolymer with the form A-B where A is a hydrophobic block selected, for example, from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyiscbutyl mcthacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate, and B is a: • hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4-vinyl pyridine), poly(dimethyl amino ethyl methacrylate), polyfdiethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolldone); • hydrophilic and anionic block, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poly(fumaric acid), poly{crotonic acid), poly(acrylamico glycolic acid) , and poly (acrylainido 2- methyipropane sulfonic acid); or • hydrophilic and non-ionic block, for example selected from: polyJPSG methacrylate); - triblock copolymer with the form A-B-C where: • A and C are different hydrophobic blocks, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate. polyisobutyl methacrylate, polyethyl nethacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate, and B is at o hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4~ vinyl pyridine), poly (dimethyl amino ethyl methacrylate), poiy(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolidone); o hydrophilic and anionic block, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(aerylamido glycolic acid), and poly(acrylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic block, tor example selected from: poly(PEG methacrylate); or * B is a hydrophobic block, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl aerylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate and A and C are different and selected from: o hydrophilic and cationic blocks, for example selected from: poly{2-vinyl pyridine), poly(4- vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate) , poly(dimethyl amino propyl methacrylamide) , and poly(N-vinyl pyrrolidone); o hydrophilic and anionic blocks, for example selected from: poly(acrylic acid), pcly(methacrylic acid), polyfmaleic acid), poly(icaconic acid), poly{fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid) and poly(acrylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic blocks, for example selected from: poly(PEG methacrylatej . 10. A composition according to the preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, adiblock copolymer with the form A-B where A is polystyrene and B is poly(2-vinyl pyridine). 11. A composition according to any preceding claim, wherein the particles having a polymeric multilayer interference structure are plate-like. 12. A composition according to any one of claims 1 to 11, wherein the particles having a polymeric multilayer interference structure include another optically- active material, for example within the amphiphilic polymer. 13. A composition, according to any one of claims 3 to 12, wherein the swelling agent is selected from: - water and organic or inorganic saline solutions with a concentration in the range 0.01 M to 5 M, for example solutions of sodium, magnesium, potassium, calcium or copper salts, solutions of phosphates and solutions of ammonium salts; - the following compounds alone, as a mixture or in aqueous solution: o glycerol, PEGs having a molecular weight in the range 400 g/mol to 50000 g/mol, mono-, di- and oligc-saccharides that are soluble in water at at least 1% by weight, sorbitol, propylene glycol, dipropylene glycol, butylene glycol, water-soluble polyols, water-irascible lower alcohols, for example methanol, ethanol or isopropanol; o neutralised or non-neutralised solutions of JV screens; and o polar oils, for example lauroyl isopropyl sarcosinate, octyldodecanol, undecane and tridecane as well as oily solutions of organic screens. 14.A method of preparing a cosmetic composition according to any one of claims 3 to 13, comprising: a) a step of bringing a swelling agent into contact with a polymeric multilayer structure having at least two layers comprising ail amphiphilic polymer; b) a step of fragmenting a film having a polymeric multilayer structure wherein at least two layers comprise an amphiphilic polymer into particles having a polymeric multilayer structure with a largest dimension of less than 100 pin and with a smallest dimension of 100 nm or more; and c) a step of dispersing the particles wich the polymeric multilayer interference structure obtained after carrying out steps a) and b) in a cosmetically acceptable medium; step b) being carried out before or after step a). 15.A non-therapeutic and in particular cosmetic method of photoprotecting human keratinous materials against, solar UV radiation, the method comprising applying a cosmetic composition according to any one of claims 1 to 13 to the human keratinous materials. 16.A photoprotective film against solar UV radiation, for application to human keratinous materials, the film including a multilayer interference structure screening solar UV radiation in which at least two layers comprise an amphiphilic polymer. 17. A photoprotective composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer. 18.A composition according to claim 17, wherein the particles of photor.ic material , in particular particles having a polymeric multilayer interference structure, have a reflection spectrum including a reflection peak in the wavelength range 250 nm to 400 nra. 19. A composition according to any one of claims 17 and 18, wherein the photonic material includes at least one swelling agent. 20.A composition according to any one of claims 17 to 19, comprising a fatty phase and an aqueous phase, the aqueous phase including particles of photonic material, in particular particles having a polymeric multilayer interference structure. 21.A composition according to any one of claims 17 to 20, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, include a fixing agent selected from inorganic materials, for example silica and its precursors, for example TEOS, glycols, for example glycerol, dipropylene glycol, sorbitol, butylene glycol, and PEGs having a molecular weight in the range 400 g/mol to 500 00 g/mol. 22. A composition according to any one cf claims 17 to 21, comprising at least two different types of pho-onic material particles, in particular particles having a polymeric multilayer interference structure, each particle type having a different transmission spectrum in the wavelength range 250 mn to 400 nm. 23. A composition according to any preceding claim, wherein the amphophilic polymer has a lamellar structure. 24.A composition according to any preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, a block copolymer. 25. A composition according to the preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, a: - difalock copolymer with the form A-B where A is a hydrophobic block selected, for example, from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate, and B is a: • hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4-vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly{diethyl amino ethyl methacrylate}, poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolidone); • hydrophilic and anionic block, for example selected from: poly(acrylic acid}, poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poIy(fumaric acid), polyfcrotonic acid), polyfacrylamido glycolic acid), and poly(acrylanido 2- methylpropane sulfonic acid); or • hydrophilic and non-ionic block, for example selected from: poly(PEG methacrylate)? - triblock copolymer with the form A-3-C where: • A and C are different hydrophobic blocks, for example selected from: polystyrene!, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate, and B is a: o hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4- vinyl pyridine), poly (dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrclidone); o hydrophilic and anionic block, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poiy(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic block, for example selected from: poly (PEG methacrylate) ,- or • B is a hydrophobic block, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl me-hacryiats, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate and A and C are different and selected from: o hydrophilic and cationic blocks, for example selected from: poly(2-vinyl pyridine}, poly{4- vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolidone); o hydrophilic and anionic blocks, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2-me-hyipropane sulfonic acid); or o hydrophilic and non-ionic blocks, for example selected from: poly(PEG methacrylate). 26. A composition according to the preceding claim, wherein the amphophilic polymer comprises, in particular consists of, a diblock copolymer with the form A-B where A is polystyrene and B is poly (2-vinyl pyridine). 27.A composition according to any one of claims 17 to 2 6, wherein the particles having a polymeric multilayer interference structure are plate-like. 28.A composition according to any one of claims 17 to 27, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, include another optically active material, for example within the amphiphilic polymer. 29.A composition according to any one of claims 19 to 28, wherein the swelling agent is selected from: - water and organic or inorganic saline solutions with a concentration in the range 0.01 M to 5 M, for example solutions of sodium, magnesium, potassium, calcium or copper salts, solutions of phosphates and solutions of ammonium salts; - zhe following compounds alone, as a mixture or in agueous solution: o glycerol, PEGS having a molecular weight in the range 400 g/mol to 50000 g/mol, mono-, di- and oligc-saccharides that are soluble in water at at least 1% by weight, sorbitol, propylene glycol, dipropylene glycol, butylene glycol, rater-soluble polyols, water-miscible lower alcohols, for example methanol, ethanol or isopropanol, benzene, acetone, ß- me-hylbutyric acid, a-ethylbutyric acid, 2,2,2,- trifluoroethanol, 1-butanol, 1,4-butanediol, chloroform, bromoethane, methyl acetate, ethyl acetate, dimethylformamide, butan-2-one, divinylbenzene, propylene glycol monomethylether acetate (PGMEA), and acetic acid solutions; o neutralized or non-neutralized solutions of UV screens; and o polar oils, for example lauroyl isopropyl sarcosinate, octyldodecanol, a C12-C15 alkylbenzoate, undecane and tridecane as well as oily solutions of organic screens. 30. A cosmetic composition comprising, in a cosmetically acceptable medium, at least particles of photonic material, in particular particles having a polymeric multilayer interference structure, as defined in any one of claims 17 to 29. 31. A method of preparing a composition according to any one of claims 19 to 30, comprising: a) a step of bringing a swelling agent into contact with a photonic material, in particular with a polymeric multilayer structure having at least two layers comprising an amphophilic polymer,- b) a step of fragmenting a film of photonic material, in particular a film having a polymeric multilayer structure wherein at least two layers comprise an amphiphilic polymer, into particles of photonic material, in particular into particles having a polymeric multilayer structure, with a largest dimension of less than 100 urn and with a smallest dimension of 103 nm or more; and c) a step of dispersing the particles of photonic material, in. particular particles having a polymeric multilayer interference structure, obtained after carrying out steps a) and b) , in a suitable medium; step b) being carried cut before or after step a). 32. A method of photoprotecting a material against solar UV radiation, the method comprising at least treating said material with a photoprotective composition according to any one of claims 17 to 30 or integrating at least said composition into said material. 33.A non-therapeutic and in particular cosmetic method of photoprotecting human keratinous materials against solar UV radiation, the method comprising at least applying a cosmetic composition according to claim 30 to human keratinous materials. 34. A method of photoprotecting an ink, a paint, or a coating, the method comprising incorporating at least one composition as defined in any one of claims 17 to 29 into said ink or said paint or said coating. 35. A method of photoprotecting a material manufactured from at least one synthetic or natural polymer, the method comprising at least treating said polymer with at least one composition as defined in any one of claims 17 to 29 or integrating at least said composition into said material. 36.A method of photoprotecting an organic or mineral glass, the method comprising at least treating said glass with at least one composition as defined in any one of claims 17 to 2 9 or integrating at least said composition into said glass. 37, a method of photoprotecting a material comprising at least sarural fibers and/or artificial fibers and/or synthetic fibers sue." as textiles or papers, the method comprising at least treating said material with at least one composition as defined in any one of claims 17 to 29 or integrating at least said composition into said material. 3 8.A film for photoprotecting against solar UV radiation, the film including a photonic material, in particular a multilayer interference structure, screening solar UV radiation wherein at least two layers comprise an amphiphilic polymer. 35.A cosmetic composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, comprising an amphiphilic polymer and producing a visible color. 40. A composition according to claim 39 having, before application to keratinous materials, a reflection spectrum including a reflection peak in the wavelength range 400 nm to 8 00 nm. 41. A composition according to claim 39 or claim 40, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, include a swelling agent. 42.A composition according to any one of claims 39 to 41, further including an additional coloring agent. 43. A composition according to the preceding claim, wherein the additional coloring agent is in the free state in the composition. 44.A composition according to any one of claims 41 to 43, wherein the swelling agent is selected from: - water and organic or inorganic saline solutions with a concentration in the range 0.01 M to 5 M, for example sodium, magnesium, potassium, calcium, or copper salts, solutions of phosphates and solutions of ammonium salts; - the following compounds alone, as a mixture or in aqueous solution: o glycerol, PEGs having a molecular weight in the range 400 g/mol to 50000 g/mol, mono-, di- and oligo-sacch.arid.es that are soluble in water at at least 1% by weight, sorbitol, propylene glycol, dipropylene glycol, butylene glycol, water-soluble polyols, water-miscible lower alcohols, for example methanol, ethanol or isopropanol, benzene, acetone, ß- methylbutyric acid, a-ethylbutyric acid, 2,2,2,- trifluoroethanol, 1-butan.ol, 1,4-butanediol, chloroform, bromoethane, methyl acetate, ethyl acetate, dimethylformamide, butan-2-one, divinylbenzene, propylene glycol monomethy1ether acetate (PGMSA), and acetic acid solutions; o neutralized or non-neutralized solutions of UV screens; and o polar oils, for example lauroyl isopropyl sarcosinate, octyldodecanol, undecane and tridecane as well as oily solutions of organic screens. 45.A composition according to any one of claims 39 to 44, wherein the coloring agent is selected from: i. liposoluble coloring agents, for example DC Red 17, DC Red 21, DC Red 27, DC Green 6, DC Yellow 11, DC Violet 2, DC Orange 5, Sudan red, carotenes such as ß- carotene or lycopene, xanthophylls such as capsanthin, capsombin or lutein, palm oil, Sudan brown, quinoline yellow, roucou, curcumin; ii. hydrosoluble coloring agents, for example FDC Red 4, DC Red 5, DC Red 22, DC Red 28, DC Red 30, DC Red 33, DC Orange 4, DC Yellow 5, DC Yellow 5, DC Yellow 8, FDC Green 3, DC Green 5, FDC Blue 1, betanin, carmine, chlorophyllin copper, methylene blue, anthocyanins, riboflavin. 46.A composition according to any one of claims 39 to 45, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, have a lamellar structure. 47. A composition according to any one of claims 39 to 46, wherein the amphiphilic polymer comprises a copolymer, in particular a block copolymer. 48. A composition according to the preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, a: - diblock copolymer with the form a-b where A is a hydrophobic block selected, for example, from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate, and E is a: • hydrophilic and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4-vinyl pyridine) , poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolldone); • hydrophilic and anionic block, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2- methylpropane sulfonic acid) ,- or •hydrophilic and non-ionic block, for example selected from: poly(peg methacrylate) ; - triblock copolymer with the form A-B-e where: • A. and C are different hydrophobic blocks selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyi methacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate, and B is a: o hyd.ropb.ilic and cationic block, for example selected from: poly(2-vinyl pyridine}, poly (4- vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacxylamide), and poly(N-vinyl pyrrclidone); o hydrophilic and anionic block, for example selected from: poly(acrylic acid), polytmethacrylic acid), poly(maleic acid), poly(itaconic acid), poly{fumaric acid), poly(crotonic acid), poly{acrylamido glycolic acid), and poly(aerylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic block, for example selected from; poly(PEG methacrylate); or • D is a hydrophobic block selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyi methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate and A and C are different and selected from: o hydrophilic and cationic blocks, for example selected from: poly(2-vinyl pyridine), poly{4- vinyl pyridine), poly (dimethyl amine ethyl methacrylate), poly(diethyl amino ethyl methacrylate) , poly (dimethyl amino propyl methacrylsirdde) , and poly (N-vinyl pyrrolidone); o hydrophilic and anionic blocks, for example selected from: poly(acrylic acid), poiyimethacrylic acid), polylmaieic acid), poiy(itaconic acid), poly(£umaric acid), poly(crotonic acid) , poly(acrylamido glycolic acid!, and poly(acrylamido 2-methylpropane sulfonic acid); or o hydrophiiic and non-ionic blocks, for example selected from: poly(PEG methacrylate). 49. A composition according to the preceding claim, wherein the amphophilic polymer comprises, in particular consists of, a ctibiock copolymer with the form A-B where A is polystyrene and B is poly (2-vinyl pyridine). 50.A composition according to any one of claims 39 to 49, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, are plate-like in form. 51. A method of making up, for example to make the complexion uniform, the method comprising applying a composition according to any one of claims 39 to 50 to human keratinous materials. 52. A film for making up; for example to make the complexion uniform, for application to human keratinous materials, the film including a photonic material, in particular a polymeric multilayer interference structure, comprising an amphiphilic polymer and producing a visible color. 53.A method of preparing a cosmetic composition according to any one of claims 41 to 5C comprising: a) a step of bringing a swelling agent into contact with a photonic material, in particular with a polymeric multilayer structure, comprising an amphiphilic polymer; b) a step of fragmenting a film of photonic material, in particular a film having a polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure, with a largest dimension of less than 100 µm and with a smallest dimension of 100 rim or more; and c) a step of dispersing the particles of photonic material, in particular particles having a polymeric multilayer interference structure, comprising an amphiphilic polymer and producing a visible color obtained after carrying out steps a) and b) in a cosmetically acceptable medium,- step b} being carried out before or after step a). 54.A cosmetic composition including particles of photonic material, in particular particles having a polymeric multilayer interference structure, including a polymer having a fluorescent agent within it. 55.A composition according to claim 54, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, have a reflection spectrum including a reflection peak in the wavelength range 250 nm to 800 nm. 5 6. A composition according to claim 54 or claim 55, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, include a swelling agent. 57. A composition according to the preceding claim, wherein the fluorescent agent is dissolved in the swelling agent. 58.A composition according to any one of claims 55 to 57, having, before application to the keratinous materials, a transmission spectrum including two minima in the wavelength range 250 nm to 8C0 nm. 59. A composition according to the preceding claim, wherein the minima are separated by at least 50 ran. 50. A composition according to claim 58 or claim 59, wherein at least one minimum is located in the wavelength range 250 nm to 400 nm arid at least one minimum is located in the wavelength range 400 run to 800 nm, for example in the range 4G0 nm tc 550 nm. 61. A composition according to any one of claims 54 to 60, wherein the fluorescent agent is an optical brightener selected from solutions of stilbene derivatives, in particular polystyry1stiibenes and triazinstiibenes, coumarin derivatives, in particular hydroxycoumarins and aminocoumarins, oxazole, benzoxazole, imidazole, triazole or pyrazoline derivatives, pyrene derivatives and porphyrin derivatives and/or mixtures thereof, and aqueous solutions of disodium distyrylbiphenyl disuifonate. 62.A composition according, to any one of claims 54 to 61, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, are plate-like. 63.A composition according to any one of claims 54 to 62, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, have a lamellar structure. 64.A composition according to any one of claims 54 to 63, wherein said amphiphilic polymer comprises a copolymer, for example a block copolymer. 65-A composition according to the preceding claim, v/herein said polymer comprises, in particular consists of, an amphiphilic polymer selected from: - diblock copolymers wi~h the form A-B where A is a hydrophobic block selected, for example, from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide, and polyisopropyl methacrylate, and B is a: • hydrophilic' and cationic block, for example selected from: poly(2-vinyl pyridine), poly(4-vinyl pyridine), poly(dimethyl amino ethyl methacrylate), poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrolidone) ,- • hydrophilic and anionic block, for example selected from: po!y(acrylic acid), poly(methacrylic acid), polyfmaleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2- methylpropane sulfonic acid) ,- or • hydrophilic and non-ionic block, for example selected from: poly(PEG methacrylate); - triblock copolymers with the form A-B-C where: • A and C are different hydrophobic blocks, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylace, polyethyl methacrylate, poly N-tert bury I acrylamide and polyisopropyl methacrylate, and B is a: o hydrophilic and cationic block, for example selected from; poiy(2-vinyl pyridine) , poly(4- vinyl pyridine), poly(dimethyl amino ethyl methacrylate) , poly(diethyl amino ethyl methacrylate) , poly(dimethyl amino propyl raethacrylamide), and poly(N-vinyl pyrrolidone]; o hydrophilic and anionic block, for example selected from: poly(acrylic acid) , poly(methacrylic acid) , polyfrraleic acid) , poly(itaconic acid), poly (f µmaric acid), poly{crotonic acid), poly[aery1amido glycolic acid), and polyfacrylamido 2-methylpropane sulfonic acid); or o hydxophilic and noil-ionic block, for example poly (PEG methacryiate); or • B is a hydrophobic block, for example selected from: polystyrene, polymethyl methacryiate, polycyclohexyl methacryiate, polyisobornyl acrylate, polyisobornyl methacryiate, polyisobutyl methacryiate, polysthyl methacryiate, poly N-tert butyl acrylamido, and polyisopropyl methacryiate and A and C are different and selected from: o hydrophilic and cationic blocks, for example selected from: poly(2-vinyl pyridine), poly{4- vinyl pyridine), poly (dimethyl amino ethyl methacryiate) , poly(diethyl amino ethyl methacryiate), poly(dimethyl amino propyl methacrylamide), and poly(N-vinyl pyrrol idone) ,- o hydrophilic and anionic blocks, for example selected from: poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(itaconic acid), poly(fumaric acid), poly(crotonic acid;, polyfacrylamido glycolic acid), and polyfacrylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic blocks, for example poly(PEG methacryiate). 66. A composition according to the preceding claim, wherein the amphophilic polymer comprises, in particular consists c£, a diblock copolymer with the form A-B where A is polystyrene and B is poly(2-vinyl pyridine}. 67 . A method of lightening human kera.tinous materials, the method comprising applying a cosmetic composition according to any one of claims 54 to 66. 68. A filir. for lightening the complexion, for application to human keratinous materials, the film including a photonic material, in particular a polymeric multilayer interference structure, comprising a polymer having a fluorescent agenc within it. 69.A method of preparing a cosmetic composition according to any one of claims 57 to 68, comprising: a) a step of bringing a swelling agent including a dissolved fluorescent agent into contact with a photonic material, in particular with a polymeric multilayer structure; b) a step of fragmenting a film of photonic material, in particular a film having said polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure, with a largest dimension of less than or equal to lOOum and a smallest dimension greater than 100 nm; and c} a step of dispersing the particles of photonic material, in particular the particles having a polymeric multilayer interference structure, obtained after carrying out steps a) and b) in a cosmetically acceptable medium; step b) being carried out before or after step a). 70. A photoprotective composition, in particular a cosmetic composition, including particles of photonic material, in particular particles having a polymeric multilayer interference structure, comprising a polymer having a UV screen within it. 71.A composition according to claim 70, wherein the particles of photonic material, in particular the particles having a polymeric multilayer interference structure, have a reflection spectrum including a reflection peak in the wavelength range 250 nm to 400 nm. 72.A composition according to claim 70 or claim 71 having, before application to the keratinous materials, a transmission spectrum including two minima in the wavelength range 250 nm to 400 nm, the minima being separated by at least 50 nm, 73.A composition according to any one of claims 7 0 to 72, having a SPF greater than or equal to 10. 74.A composition according to any one o£ claims 7 0 to 73, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, have a lamellar structure. 75.A composition according to any one of claims 70 to 74, wherein said polymer comprises a copolymer, in particular a block copolymer. 76.A composition according to the preceding claim, wherein said polymer comprises, in particular consists of, a: - dibiock copolymer with the form A-B where A is a hydrophobic block selected, for example, from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobomyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N- tert butyl acrylamide, and polyisopropyl methacrylate, and B is a: » hydrophilic and cationic block, for example selected from: poly{2-vinyl pyridine), poly{4-vinyl pyridine) , poly(dimethyl amino ethyl methacrylate) , poly(diethyl amino ethyl methacrylate), poly(dimethyl amino propyl methacryiamide), and poly(N-vinyl pyrrolidonel; • hydrophilic and anionic block, for example selected from: poly (acrylic acid), poly (raethacrylic acid), poiy(maleic acid), poly(itaconic acid), poly(fumaric acid), poly (crotonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2- methylpropane sulfonic acid); or • hydrophilic and non-ionic block, for example selected from: poly(PEG methacrylate); - triblock copolymer with the form A-B-C where: • A and C are different hydrophobic blocks, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate, and B is a: o hydrophilic and cationic block, for example selected from,- poly(2-vinyl pyridine), poly(4- vinyl pyridine), poly{dimethyl amino ethyl methacrylate) , poly(diethyl amino ethyl methacrylate) , poly (dimethyl amino propyl metbacrylamide) , and poly(N-vinyl pyrrolidone); o hydrophilic and anionic block, for example selected from: polyiacrylic acid), poly(methacrylic acid), poly(maleic acid), poly (itaconic acid), poly(fnmaric acid), poly(crotonic acid), poly(acrylamido glycolic acid), and poly (acrylamido 2-methylpropane sulfonic acid); or o hydrophilic and non-ionic block, fcr example poly(PEG methacrylate); cr • B is a hydrophobic block, for example selected from: polystyrene, polymethyl methacrylate, polycyclohexyl methacrylate, polyisobornyl acrylate, polyisobornyl methacrylate, polyisobutyl methacrylate, polyethyl methacrylate, poly N-tert butyl acrylamide and polyisopropyl methacrylate and A and C are different and selectee from: o hydrophilic and cationic blocks, for example selected from: poly(2-vinyl pyridine), poly(4- vinyl pyridine), poly (dimethyl amino ethyl methacrylate) , poly(diethyl amino ethyl methacrylate), poly (dimethyl amino propyl -nethacrylamide) , and poly(N-vinyl pyrrolidone) ,- o hydrophilic and anionic blocks, for example selected from: poly(acrylic acid), poly{methacrylic acid), polyimaleic acid), poly(itaconic acid), polylfumaric acid), poly(crctonic acid), poly(acrylamido glycolic acid), and poly(acrylamido 2-metnylpropane sulfonic acid); or o hydrophilic and non-ionic blocks, for example poly(PEG methacrylate) . 77. A composition according to the preceding claim, wherein the amphiphilic polymer comprises, in particular consists of, a diblock copolymer with the form. A-3 where A is polystyrene and 3 is poly(2-vinyl . pyridine). 78.A composition according to any one of claims 70 to 77, wherein the particles of photonic material, in . particular particles having a polymeric multilayer interference structure, include a swelling agent. 79. A composition according to the preceding claim, wherein the UV screen is dissolved in the swelling agent. SO. A composition according to any preceding claim, wherein the UV screen is selected from: - hydrophobic screens, for example: dibenzoylmethane derivatives, aminobenzophenones, anthranilic derivatives, 4,4-diarylbutadiene derivatives, para- aminobenzoates, salicylic derivatives, cinnamates, ß, ß -diphenyiacrylate derivatives, benzylidene camphor derivatives, triazine derivatives, imidazoline derivatives, benzalmalonate derivatives, merocyanin derivatives, benzophenone derivatives, phenyl ben20triazols derivatives, bis-resorcinyl triazine derivatives and benzoxazole derivatives; and - hydrosoluble screens, for example: terephthalylidene dicamphor sulfonic acid, bis- bensoazolyl derivatives, p-aminobenzoic acid (PABA) derivatives and benzophenone derivatives comprising at least one sulfonic radical. 81.A composition according 10 any one of claims 70 to 80, wherein the particles of photonic material, in particular particles having a polymeric multilayer interference structure, are plate-like. 82 . A cosmetic composition comprising, in a cosmetically acceptable medium, at least particles of photonic material, in particular particles having a polymeric multilayer interference structure, as defined in any one of claims 7 0 to 81. 83. A method of preparing a composition according to any one of claims 70 to 82, comprising: a) a step of bringing a swelling agent including a dissolved UV screen into contact with a photonic material, in particular with a polymeric multilayer structure; b) a step cf fragmenting a film of photonic material, in particular a film having said polymeric multilayer structure, into particles of photonic material, in particular into particles having a polymeric multilayer structure with a largest dimension of less than 100µm and a smallest dimension greater than 100 nm; and c) a step of dispersing the particles of phoronic material, in particular particles having a polymeric multilayer interference structure, obtained after carrying out steps a) and b} in a suitable medium; step b) being carried out before or after step a). 84.A method of photoprotecting a material against solar UV radiation, the method comprising treating said material with a photoprotective composition according to any one of claims 70 to 82 or integrating at least said composition into said material. 85.A method of non-therapeutic and in particular cosmetic photoprotection of human keratinous materials against solar UV radiation, the method comprising applying a cosmetic composition according to claim 82 to human keratinous materials. 86. A method of photoprotecting an ink, a paint, or a coating, the method comprising incorporating at least one composition as defined in any one of claims 70 to 82 into said ink or paint or said coating. 87. A method of photoprotecting a material manufactured from at least one synthetic or natural polymer, the method comprising treating said polymer with at least one composition as defined in any one of claims 7G to 82 or integrating at least said composition into said material. 88.A method of photoprotecting an organic or mineral glass, the method consisting in treating said glass with at least one composition as defined in any one of claims 70 to 82 or integrating at least said composition into said glass. 89. A method of photoprotecting a material comprising at least natural fibers and/or artificial fibers and/or synthetic fibers such as textiles or papers, the method comprising treating said material with at least one composition, as defined in any one of claims 7 0 to 82 or integrating at least said composition into said material. 90.A film that photoprotects against solar UV radiation, the film including a photonic material, in particular a multilayer interference structure screening solar UV radiation, wherein at least two layers comprise an amphiphilic polymer having a UV screen within it. ABSTRACT The present invention provides a photoprotective composition, in particular a cosmetic composition, including particles of photonic material in particular having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer. The invention provides a method of photoprotecting a material against solar UV radiation, the method consisting in treating said material with a photoprotective composition including particles of photonic material in particular having a polymeric multilayer interference structure, at least two layers of said structure comprising an amphiphilic polymer or integrating at least said composition into said material. Said material may in particular be selected from inks, paints, glasses, textiles, papers and polymers. The invention also provides a film that photoprotects against solar UV radiation, the film including a photonic material in particular having a multilayer interference structure screening solar UV radiation, wherein at least two layers comprise an amphiphilic polymer.