The invention relates to (I) a process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated in several steps, comprising at least one step E1 ) of dyeing said fibres using a cosmetic dye composition A comprising i) indigo-producing plant powder and/or an indigo-producing plant dye extract and optionally henna, ii) at least one step E2) of post-treatment of said fibres using an aqueous cosmetic composition B whose pH is less than 7, comprising one or more particular natural dyes iii), other than henna and indigoids, and iv) one or more acidifying agents; composition A preferably being applied first to the keratin fibres; and composition B being applied to the keratin fibres after application of composition A, and to (II) the use of an acidic aqueous composition B, comprising one or more particular natural dyes, for accelerating the stabilization over time (on the day of performing the dyeing process) of the colour of the fibres dyed with indigo and optionally henna and for improving the intensity, the colour buildup and/or the colour persistence thereof.

Specifically, colourings produced using indigo and optionally henna are generally evolutive over time in terms of colour: they have a characteristic yellow/green colouring on the day of application (i.e. on the day of dyeing). This relatively unaesthetic "raw" colour, which is little appreciated by dye users, changes towards the desired colourings after a few hours (48 hours to 1 week) and may change in colour over time (appearance of violet-red tints generally after 2 to 3 weeks). There is thus a need to stabilize this colouring to obtain an aesthetic colouring on the day of application (for example brown free of yellow/green tints) which changes little over time (no colour change) while at the same time respecting the integrity of the keratin fibres.

Two major methods for dyeing human keratin fibres, and in particular the hair, are known.

The first, known as oxidation dyeing or permanent dyeing, consists in using one or more oxidation dye precursors, more particularly one or more oxidation bases optionally combined with one or more couplers.

Usually, oxidation bases are selected from ortho- or para-phenylenediamines, ortho- or para-aminophenols, and heterocyclic compounds. These oxidation bases are colourless or weakly coloured compounds, which, when combined with oxidizing products, can give rise via a process of oxidative condensation to coloured species, which remain trapped within the fibre.

The shades obtained with these oxidation bases are often varied by combining them with one or more couplers, these couplers being chosen in particular from aromatic meta-diamines, meta-aminophenols, meta-diphenols and certain heterocyclic compounds, such as indole compounds.

The variety of molecules used as oxidation bases and couplers allows a wide range of colours to be obtained.

The second dyeing method, known as direct dyeing or semi-permanent dyeing, comprises the application of direct dyes, which are coloured and colouring molecules that have affinity for fibres. Given the nature of the molecules used, they tend rather to remain on the surface of the fibre and penetrate relatively little into the fibre, when compared with the small molecules of oxidation dye precursors. The main advantages of this type of dyeing are that it does not require any oxidizing agent, which limits the degradation of the fibres, and that it does not use any dyes that have particular reactivity, resulting in limitation of the intolerance risks.

The first hair dyes were semi-permanent. One of the most widely-known natural dyes is indigo (see Ullmann's Encyclopedia of Industrial Chemistry, "Hair preparation", point 5.2.3, 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim; 10.1002/14356007.a12 571.pub2). Indigo continues to be used in female beauty enhancement for dyeing the hair or the nails, or for dyeing fabrics (jeans), leather, silk, wool, etc. Indigo [482-89-3] is a natural blue dye, and its isomer indirubin is red. Their empirical formula is: C16H10N2O2; and their chemical structures are the following:

Indigo Indirubin

Depending on the oxidation/overoxidation, isatin may give indigotin or indirubin (Maugard et al., 2001 ). The presence of these two isomers accounts for the violet colour of indigo that is more or less pronounced as a function of the respective proportion in the hair of the two isomers formed in the hair (in particular violet to purple if the amount of indirubin increases).

Indigo is derived from indican and may be prepared from various plants known as indigo-producing plants such as Indigofera tinctoria, Indigo suffruticosa, Polygonum tinctorium etc. (see Kirk-Othmer Encyclopedia of Chemical Technology, updated on 17/04/2009, DOI: 10.1002/0471238961 .0425051903150618. a01.pub2). The indigo-producing plants are generally chopped and soaked in hot water, heated, fermented and oxidized in the open air to liberate the purple-blue coloured indigo (see Chem. Rev. 201 1 , 111 , 2537-2561 , pages 2537-2561 ). Indigo is the result of the hydrolysis and then oxidization of indican (glycosyl precursor).

The problem is that dyeing using the indigo leaf is difficult because the dyeing kinetics in the keratin fibres is variable. Furthermore, the dyeing process is unstable. Indigo theoretically affords a blue colouring on grey hair, and a "cold" colour of ash type. However, the dyeing process using indigo is difficult to control due to the competing reaction for the formation of indirubin (which also involves an oxidation step with intermediate formation of yellow-coloured isatin) giving yellow to dark purple tints complementary to chestnut-brown hair over time.

The colourings resulting from mixtures of indigo and henna are thus generally evolutive over time in terms of colour, they have a characteristic yellow/green colour on the day of dyeing (relatively unaesthetic "raw" colour, which dye users appreciate little) which changes towards the desired colourings after a few hours (48 hours to 1 week) and may change colour over time

(appearance of violet-red tints generally after 2 to 3 weeks). There is thus a need to stabilize this colouring to obtain an aesthetic colouring on the day of application (for example brown free of yellow/green tints) which changes little over time (no colour change).

To overcome this problem of the relatively unaesthetic colouring on the day of dyeing and of changing of the colour, it is known practice to "dope" the dyeing by adding direct dyes to mask the undesirable tints, these dyes generally being used in direct dyeing, such as nitrobenzene, anthraquinone, nitropyridine, azo, methine, azomethine, xanthene, acridine, azine or triarylmethane direct dyes (see, for example, EP 0 806 199). This option has the drawback for natural product users, or for partisans of "natural/bio" products, in that the colouring is partly performed using synthetic dyes. However, the tint provided on the day of application does not prevent the colour change over time (evolution of the yellow tint that is still present in the fibre, although masked, towards red).

Moreover, the colourings obtained with indigo are not always homogeneous between the root and the end or from one fibre to another ( The Science of Hair Care, C. Bouillon, J. Wilkinson, 2nd Ed., CRC Press, Taylor & Francis Group; Boca Raton, Florida, pages 236-241 (2005)).

Finally, the indigo molecule is insoluble in water, and so when a mixture of indigo and henna, which itself is water-soluble, is used, this leads to substantial inhomogeneities in colour buildup between the root and the end (selectivity).

There is thus a real need to develop dyeing processes that make it possible to obtain powerful, aesthetic and natural colourings from the end of application, while at the same time respecting the cosmetic properties of the keratin fibres, and which make it possible especially to obtain rapid colourings, of which the colouring obtained has no yellow/green tints that are considered by users to be unaesthetic, and which have improved colour buildup, are less aggressive to the hair and at the same time are resistant to external agents (light, bad weather, shampooing), which are persistent and/or homogeneous while at the same time remaining powerful and/or chromatic, and which do not change in colour over time (in particular towards red tints).

This aim is achieved by the present invention, one subject of which is a process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated in several steps, comprising:

- at least one step E1 ) of dyeing said fibres using a cosmetic dye composition A comprising indigo-producing plant powder and/or extract i) and optionally henna ii);

- at least one step E2) of treating said fibres using an aqueous cosmetic composition B whose pH is less than 7 and comprising one or more natural dyes iii) chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D and/or kermesic acid;

iii-ii) betalains, preferably betanin;

iii-iii) anthocyanidins (also known as anthocyanides or anthocyanidols), preferably of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

iii-iv) carthamine;

iii-v) naphthoquinones comprising at least two hydroxyl groups, preferably at least three hydroxyl groups, preferably chosen from alkanine (also known as Orcanette) and/or shikokine;

and mixtures thereof;

and iv) one or more acidifying agents;

- it being understood that, preferably, composition A is applied first to the keratin fibres; and that composition B is applied to the keratin fibres after the application of composition A;

- the process preferably involving at least one rinsing step and/or one washing step between the dyeing step using composition A and the treatment step involving the application of composition B.

Thus, according to a preferred embodiment, the dyeing process according to the invention involves a first step of dyeing the keratin fibres via the application of a dye composition A to the fibres, comprising indigo-producing plant powder and/or extract and optionally henna, followed by a step of treating with an aqueous composition B whose pH is less than 7, comprising one or more particular natural dyes as defined previously and one or more acidifying agents, i.e. in post-treatment.

According to another embodiment, the dyeing process according to the invention involves a step of treating with an aqueous composition B whose pH is less than 7, comprising one or more particular natural dyes as defined previously and one or more acidifying agents, followed by a step of dyeing the keratin fibres via the application of a dye composition A to the fibres, comprising indigo-producing plant powder and/or extract and optionally henna.

A subject of the invention is also the use of an aqueous composition B whose pH is less than 7, comprising one or more particular natural dyes iii), as defined previously, and iv) one or more acidifying agents, to accelerate the stabilization of the colour of fibres dyed with indigo, and optionally henna, over time and to improve the colour intensity and/or the colour buildup and/or the colour persistence.

The process for dyeing keratin fibres according to the invention has the advantage of dyeing said fibres, especially human keratin fibres, in particular the hair, with natural dyeing results without any yellow/green tints, and/or powerful, chromatic colourings, which are resistant to washing, perspiration, sebum and light, and which are moreover long-lasting, without impairment of the fibre. Furthermore, the colourings obtained using the process are uniform from the root to the end of a fibre (little colour selectivity). The treated keratin fibres show very good cosmetic properties; in particular, their integrity is respected and they have a great level of sheen.

The compositions used according to the invention are cosmetic compositions, i.e. they

are cosmetically acceptable and are thus suitable for use for application to keratin fibres, especially for application to human keratin fibres such as the hair.

Preferably, composition A is obtained by mixing, just before use, indigo-producing plant powder i) and optionally henna ii) with an aqueous composition to obtain a ready-to-use dye composition A, preferably in the form of a poultice.

Preferably, composition A is an aqueous composition.

i) indigo-producing plant powder and/or extract

The dye composition A according to the invention comprises indigo-producing plant powder and/or extract. (For the purposes of the present invention, the term "indigo-producing plant extract" means "a dye extract from an indigo-producing plant").

As indigo-producing plants, mention may be made of numerous species derived from the following genera:

- Indigofera such as Indigofera tinctoria, Indigo suffruticosa, Indigofera articulata,

Indigofera arrecta, Indigofera gerardiana, Indigofera argenta, Indigofera indica, Indigofera longiracemosa]

- Isatis such as Isatis tinctoria;

- Polygonum or Persicaria such as Polygonum tinctorium (Persicaria tinctoria)

- Wrightia such as Wrightia tinctoria]

- Calanthe such as Calanthe veratrifolia] and

- Baphicacanthus such as Baphicacanthus cusia.

Preferably, the indigo-producing plant is of the genus Indigofera and more particularly is Indigofera tinctoria, suffruticosa or argentea, preferably Indigofera tinctoria.

Use may be made of all or part (in particular the leaves especially for Indigofera tinctoria ) of the indigo-producing plant.

The indigo-producing plant powder may be screened to obtain particles with upper limit sizes corresponding to the orifices or mesh sizes of the screen particularly between 35 and 80 mesh (US).

According to a particular mode of the invention, the size of the indigo-producing plant powder particles is fine. According to the invention, a particle size of less than or equal to 500 pm is more particularly intended. Preferentially, the powder is constituted of fine particles with sizes inclusively between 50 and 300 pm and more particularly between 10 and 200 pm.

It is understood that said indigo-producing plant particles preferentially have a moisture content of between 0 and 10% by weight relative to the total weight of the powders.

The indigo-producing plant extract according to the invention is a product of maceration in solvents, generally organic solvents, of all or part (in particular the leaves especially for Indigofera tinctoria ) of the indigo-producing plant.

The indigo-producing plant powder according to the invention is a natural product originating from indigo-producing plants, reduced by grinding or other mechanical means into

fine particles.

Preferably, an indigo-producing plant powder is used.

According to a particular embodiment of the invention, composition A is in the form of a solid, preferably pulverulent, preferably anhydrous composition. According to this embodiment, the indigo-producing plant powder is preferably present in composition A in a content ranging from 10% to 99% by weight, relative to the total weight of composition A, more particularly ranging from 20% to 90% by weight, preferentially ranging from 20% to 80% by weight.

According to another particular embodiment of the invention, composition A is obtained by mixing just before use (i.e. extemporaneously) the indigo-producing plant powder and/or extract i) and optionally henna ii) with water or with an aqueous composition to obtain a ready-to-use dye composition A, preferably in the form of a poultice.

According to this embodiment, the indigo-producing plant powder and/or extract is present in composition A preferably in a content ranging from 0.5% to 50% by weight, relative to the total weight of composition A, when composition A is aqueous, more particularly ranging from 1 % to 40% by weight, preferentially ranging from 5% to 30% by weight.

According to a particularly preferred embodiment, when it is ready-to-use, composition A comprises water.

It is then preferably aqueous. The term "ready-to-use" refers to a composition that is ready to be applied directly to the keratin fibres.

According to a particular embodiment of the invention, composition A of the invention may also contain one or more surfactants, preferably anionic or nonionic surfactants.

The ready-to-use composition A applied to the keratin fibres according to the process of the invention is preferably obtained from mixing between the indigo-producing plant powder and/or extract i) in compact or loose form, optionally henna ii), and an aqueous composition, preferably water.

Preferably, the ready-to-use composition A applied to the keratin fibres according to the process of the invention is in the form of a poultice.

Preferably, the ready-to-use dye composition A comprises a water content ranging from 10% to 99% by weight, more particularly from 20% to 98% by weight and better still from 40% to 95% by weight relative to the weight of ready-to-use composition A.

To do this, the indigo-producing plant powder or extract i), optionally the henna ii) and optionally the additional compounds as described previously are mixed with an aqueous composition comprising water, to obtain a poultice of creamy and pleasant consistency corresponding to the ready-to-use composition A. When the indigo-producing plant powder is compact, it is crumbled into the aqueous composition, and the compact composition is preferentially crumbled into water.

Henna ii)

The dye composition A) according to the invention preferably comprises henna ii).

According to the present invention, the term "henna" refers to a henna plant powder and/or a henna plant dye extract, preferably from a henna plant such as Lawsonia alba or Lawsonia inermis. The henna plant powder and/or dye extract especially comprises lawsone and/or a glucosylated precursor thereof.

Preferably, the henna used according to the present invention is in powder form.

It is understood that the "henna powder" and the indigo-producing plant powder are different from an extract. Specifically, an extract is a product of maceration in solvents, generally organic solvents, whereas the powder according to the invention is a natural product originating from henna or indigo-producing plants, reduced by grinding or other mechanical means, into fine particles.

The henna used in the invention is preferably red henna ( Lawsonia inermis, alba). Lawsone [83-72-7] (Cl Natural Orange 6; Cl 75420), also known as isojuglone, may be found in henna shrubs ( Lawsonia alba, Lawsonia inermis). Preferably, the henna is in powder form. The henna powder may be screened to obtain particles with upper limit sizes corresponding to the orifices or mesh sizes of the screen particularly between 35 and 80 mesh (US). According to a particular mode of the invention, the size of the henna powder particles is fine. According to the invention, a particle size of less than or equal to 500 pm is more particularly intended. Preferentially, the powder is constituted of fine particles with sizes inclusively between 10 and 300 pm and more particularly between 50 and 250 pm. It is understood that said henna particles preferentially have a moisture content of between 0 and 10% by weight, relative to the total weight of the powders.

Preferably, said henna particles are derived from henna leaves.

As indicated previously, according to a particular embodiment of the invention, composition A is in the form of a solid, preferably pulverulent, preferably anhydrous composition. According to this embodiment, henna is preferably present in composition A in a content ranging from 5% to 99% by weight, relative to the total weight of composition A, more particularly ranging from 10% to 60% by weight, preferentially ranging from 15% to 40% by weight, in particular when composition A is anhydrous.

As indicated previously, according to another particular embodiment of the invention, composition A is obtained by mixing just before use (i.e. extemporaneously) the indigo-producing plant powder i) and henna ii) (when it is present) with water or with an aqueous composition to obtain a ready-to-use dye composition A, preferably in the form of a poultice.

According to this embodiment, henna is present in composition A preferably in a content ranging from 0.1 % to 30% by weight, relative to the total weight of composition A, when composition A is aqueous, more particularly ranging from 0.15% to 20% by weight, preferentially ranging from 0.2% to 10% by weight.

Preferably, when the dyeing process according to the invention uses henna, then the indigo-producing plant powder and/or extract i) and henna ii) are present in composition A in a i)/ii) weight ratio ranging from 0.1 to 95, preferably from 0.5 to 50 and better still from 1 to 10.

Composition B:

Composition B used according to the invention is an aqueous composition whose pH is less than 7. Preferably, the pH of composition B is less than 6, and preferably less than 5.0.

Preferably, the pH of composition B used according to the invention is inclusively between 0.5 and 5, more particularly between 0.5 and 4.5, preferably between 2 and 4.

Composition B according to the invention comprises iv) one or more acidifying agents, preferably chosen from mineral or organic acids such as hydrochloric acid, orthophosphoric acid, sulfuric acid, carboxylic acids such as acetic acid, alpha-hydroxycarboxylic acids (AHA) such as citric acid and lactic acid; and mixtures thereof.

In particular, the pH of composition B may be adjusted to the desired value by means of acidifying agents as described above, or alternatively using standard buffer systems.

According to a particular embodiment of the invention, composition (A) comprises at least one acid, preferably chosen from mineral acids, which are preferably chosen from hydrochloric acid, phosphoric acid and sulfuric acid and the conjugate salts thereof, in particular phosphoric acid and the salts thereof.

Preferably, composition (B) comprises an inorganic buffer system comprising at least one mineral (inorganic) acid and the conjugate base thereof, i.e. the inorganic salt of said inorganic acid. Preferably, composition (B) comprises an inorganic buffer system comprising a mixture of at least phosphoric acid (H3PO4) and at least one inorganic phosphate salt, in particular chosen from potassium dihydrogen phosphate KH2PO4, sodium dihydrogen phosphate NaH2PC>4, dipotassium hydrogen phosphate K2HPO4, disodium hydrogen phosphate Na2HPC>4, potassium hydrogen phosphate K3PO4 and sodium phosphate Na3PC>4, and mixtures thereof.

The acidifying agent(s) iv) as defined previously preferably represent from 0.001 % to 15% by weight relative to the weight of composition B, more particularly, from 0.005% to 10% by weight relative to the weight of composition B, better still from 0.5% to 5%.

Preferably, the acidifying agent(s) iii) are present in the aqueous composition B in a concentration inclusively between 0.1 M and 1 M, such as 0.5 M.

Natural dyes iii) present in composition B:

Composition B used according to the invention comprises one or more natural dyes iii) chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function,

preferably chosen from carminic acid, laccaic acid and/or kermesic acid; iii-ii) betalains, preferably betanin;

iii-iii) anthocyanidins (also known as anthocyanides, or anthocyanidols) preferably of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

iii-iv) carthamine;

iii-v) naphthoquinones comprising at least two hydroxyl groups, preferably at least three hydroxyl groups, preferably chosen from alkanine (also known as Orcanette) and/or shikokine;

and mixtures thereof.

According to an advantageous embodiment of the invention, the natural dye(s) iii) are chosen from anthraquinones comprising at least two hydroxyl groups, preferably chosen from alizarin, xanthopurpurin, rubiadin, lucidin, munjistin, anthragallol, purpurin, pseudopurpurin and morindone, and mixtures thereof, preferably at least three hydroxyl groups, preferably chosen from anthragallol, purpurin, pseudopurpurin, morindone and munjistin, and mixtures thereof.

Preferably, the anthraquinone(s) are dyes that absorb in the red region.

According to an advantageous embodiment of the invention, the natural dye(s) iii) are compounds comprising at least one carboxylic acid function.

Preferably, according to this embodiment, the natural dyes iii) are preferably chosen from:

- iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betalains, preferably betanin;

and mixtures thereof.

According to another advantageous embodiment of the invention, the natural dye(s) iii) are chosen from:

iii-iii) anthocyanidins (also known as anthocyanides, or anthocyanidols) preferably of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof.

Included among the natural dyes used according to the invention are compounds that

may be present in nature and that are reproduced by chemical (semi)synthesis.

The natural dye(s) according to the invention may or may not be salified. They may also be in aglycone form (without bonded sugars) or in the form of glycosylated compounds.

The term "glycosyl radical" means a radical derived from a monosaccharide or polysaccharide.

The natural dyes according to the invention may be in the form of powders or liquids. Preferably, the natural dyes of the invention are in the form of powders.

Preferably, the natural dyes used according to the invention in composition B have an absorption wavelength l™3c of between 625 and 750 nm or between 300 and 470 nm, and better still between 625 and 750 nm.

Preferably, the dyes of the invention are dyes which absorb in the red range, i.e. at an absorption wavelength which is within the range particularly between 300 and 470 nm, or in the violet range between 625 and 750 nm of red-orange, preferably reds.

In particular, according to a first preferred embodiment of the invention, the natural dye(s) iii) are anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from those of formula (A1) below, comprising at least one carboxylic acid function:

and also the tautomeric and/or mesomeric forms thereof, the stereoisomers thereof, the addition salts thereof with a cosmetically acceptable acid or base, and the solvates thereof such as hydrates;

in which formula (A1):

• R1 and R8, which may be identical or different, represent a hydrogen atom, a hydroxyl group or an alkyl group such as methyl;

• R2 represents a hydrogen atom or a hydroxyl group, carboxyl group -C(0)OH or carboxylate group -C(0)0 , Q+ with Q+ representing an alkali metal or alkaline-earth metal such as potassium or calcium;

• R3 represents i) a hydrogen atom, ii) a hydroxyl group or iii) an optionally substituted aryl group, preferably a phenyl group optionally substituted with one or more groups chosen from a) hydroxyl, b) amino, c) (Ci-C6)alkyl optionally substituted with one or more groups chosen from hydroxyl, carboxyl and (Ci-C4)alkylcarbonylamino;

• R4 represents a hydrogen atom or a hydroxyl group;

• R5 represents a hydrogen atom, or a hydroxyl, carboxyl or carboxylate group -C(0)0-, Q+ with as defined previously;

• R6 represents a hydrogen atom, a hydroxyl group, -O , Q+ with Q+ as defined previously, carboxyl or carboxylate group -C(0)0 , Q+ with Q+ as defined previously;

• R7 represents a hydrogen atom, a hydroxyl group or a glycosyl radical, preferably glucose.

Preferentially, the dyes of the invention are of formula (A1 ) and in particular, taken together or separately in which:

■ R1 represents a hydroxyl or (Ci-C4)alkyl group;

■ R2, R4 and R8, which may be identical or different, represent a hydrogen atom or a hydroxyl group;

■ R3 represents a hydrogen atom, a hydroxyl group or a phenyl group optionally substituted with one or more groups chosen from hydroxyl, carboxyl and (Ci- C4)alkylcarbonylamino such as:

with Y representing a group chosen from: -CH(NH2)-C(0)0H, -CH2-OH, -NH-C(0)-CH3; and "— ^
the point of attachment to the rest of the molecule.

• R5 and R6, which may be identical or different, represent a hydrogen atom or a hydroxyl group, carboxyl group -C(0)0H or carboxylate group -C(0)0 , CTwith Q+ representing an alkali metal or alkaline-earth metal such as potassium or calcium; and

• R7 represents a hydrogen atom or a hydroxyl group.

According to one embodiment, the dye(s) of the invention are of formula (A1): and in particular, taken together or separately in which:

■ R1 represents a (Ci-C4)alkyl group;

■ R2 represents a carboxyl or carboxylate group -C(0)0 , Q+ with Q+ representing an alkali metal or alkaline-earth metal such as potassium or calcium;

■ R3 and R8 represent a hydroxyl group;

■ R4 represents a hydrogen atom or a hydroxyl group, preferably hydrogen;

■ R6 represents a hydroxyl group or -O , Q+ with Q+ as defined previously; and

• R7 represents a hydrogen atom or a glycosyl radical such as glucose.

The natural dyes iii) are particularly preferably chosen from anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D (also known as flavokermesic acid), pseudopurpurin and munjistin, and mixtures thereof; preferably from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C and laccaic acid D, preferably laccaic acid D and/or kermesic acid.

The structures of these compounds are as follows:

Preferably, the natural dyes iii) are chosen from carminic acid, laccaic acid D or kermesic acid, pseudopurpurin and munjistin, and mixtures thereof.

According to a second advantageous embodiment of the invention, the natural dye(s) iii) are chosen from betalains, preferably betanin. Betalains are dyes derived from beetroot.

According to a third advantageous embodiment of the invention, the natural dye(s) iii) are chosen from anthocyanidins (also known as anthocyanides, or anthocyanidols) preferably of formula (Vg) which include at least three hydroxyl groups; preferably chosen from cyanidol, cyanidin, delphinidin, pelargonin, malvidin, peonidin, petunidin, aurantinidin and luteolinidin, and mixtures thereof, heterosides thereof such as dihydroxyanthocyans (or dihydroxyanthocyanosides, or anthocyanins), oligomers and polymers thereof such as proanthocyanins; preferably anthocyanidols and especially extracts of blackcurrant, blueberry, radish, grape, red cabbage, elderberry, black carrot and black rice; preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof.

According to an advantageous embodiment of the invention, the natural dye(s) iii) are chosen from the anthocyanidins (also known as anthocyanides, or anthocyanidols) of formula (Vg) below, which preferably include at least three hydroxyl groups:

in which formula (Vg):

• R1, R2, R3, R4, R10, R11, R12, R13 and R14, which may be identical or different, represent a hydrogen or halogen atom or a group chosen from i) hydroxyl, ii) (Ci-C6)alkyl, iii) (Ci-C6)alkoxy, iv) (Ci-C6)alkylthio, v) carboxyl, vi) alkyl or alkoxycarbonyl carboxylate, vii) optionally substituted amino, viii) optionally substituted linear or branched alkenyl, ix) optionally substituted cycloalkyl, x) optionally substituted aryl, xi) a group containing one or more silicon atoms, xii) (di)((hydroxy)(Ci-C6)alkyl)amino, xiii) glucosyl, xiv) R-Z-C(X)-Y- with R representing a hydrogen atom or a (Ci-C6)alkyl or aryl group that is optionally substituted, especially with at least one hydroxyl group, such as 3,4,5-trihydroxyphenyl; Y and Z, which may be identical or different, represent a bond or an oxygen or sulfur atom or a group -N(R’)-with R’ representing a hydrogen atom or a (Ci-C6)alkyl group, Y also possibly representing a (Ci-C6)alkylene group; X representing an oxygen or sulfur atom or N-R” with R” representing a hydrogen atom or a (Ci-C6)alkyl group;

• R6 and R8, which may be identical or different, represent a hydrogen atom or a group chosen from a hydroxyl group, a (Ci-C6)alkyl group or a group R-Z-C(X)-Y- as defined previously;

• or alternatively the unit (V) constitutes the polymeric unit of a polyphenol which will be linked to the other units of said polyphenol via positions 4, 6 or 8 of the chroman ring, in which case R1, or R3 and R6 form a covalent bond with the other units of said polyphenol;

it being understood that at least three radicals of the compounds of formula (Vg) chosen from R1, R2, R3, R4, R8, R10, R11, R12, R13 and R14 represent a hydroxyl group;

the compound of formula (Vg) being cationic and is associated with an organic or mineral anionic counterion An , such as halide.

Preferably, the radicals R1 , R6, R14 and R10 represent a hydrogen atom.

Preferably, the group R-Z-C(X)-Y- of the compounds of formula (V) represents a 3,4,5-trihydroxyphenyl-1-carbonyloxy (-O-gallate). Preferably, the radicals Ri, R2, R3, R4, R10, R11, R12, R13 and R-u are chosen from a hydrogen atom and hydroxyl, glycosyloxy and alkoxy groups.

According to a particularly preferred embodiment of the invention, the natural dyes iii) are anthocyanidins of formula Vg, in which the radicals R1 , R6, R14 and R10 represent a hydrogen atom.

The other radicals R2, R3, R4, R8, R13, R12 and R11 include at least four hydroxyl and/or alkoxy functions (preferably methoxy), better still at least five hydroxyl and/or methoxy functions.

According to a preferred embodiment of the invention, the natural dyes iii) are anthocyanidins of formula Vg chosen from the compounds mentioned in the table below, and mixtures thereof.

According to a preferred embodiment of the invention, the natural dyes iii) are anthocyanidins chosen from cyanidin, delphinidin, malvidin, peonidin and petunidin, and mixtures thereof.

According to a preferred embodiment of the invention, the natural dyes iii) are chosen from anthocyanidins chosen from delphinidin, malvidin and petunidin, and mixtures thereof.

According to a fourth advantageous embodiment of the invention, the natural dye(s) iii) are chosen from carthamine.

According to a fifth advantageous embodiment of the invention, the natural dye(s) iii) are chosen from naphthoquinones comprising at least two hydroxyl groups, preferably at least three hydroxyl groups, preferably chosen from alkanine (also known as Orcanette) and/or shikokine.

According to a preferred embodiment, the natural dyes iii) used according to the present invention are polyphenols (and/or polyphenols-rich extracts).

The term "polyphenol" means a compound comprising in its structure several hydroxyl functions borne on one or more 6-membered carbon-based aromatic rings.

According to this embodiment, the natural dye(s) iii) used according to the present invention are polyphenols chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D and/or kermesic acid;

iii-ii) betalains, preferably betanin;

iii-iii) anthocyanidins (also known as anthocyanides or anthocyanidols), of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

iii-iv) carthamine;

and mixtures thereof.

According to another advantageous embodiment of the invention, the natural dye(s) iii) are compounds comprising at least one carboxylic acid function.

Preferably, according to this embodiment, the natural dyes iii) are chosen from:

- iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betalains, preferably betanin;

and mixtures thereof.

Preferably, the natural dye(s) iii) are chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D and/or kermesic acid, pseudopurpurin and munjistin;

betanin.

Preferably, the natural dye(s) iii) are chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betanin;

and mixtures thereof.

Even more preferably, the natural dye(s) iii) are chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid.

In the context of the present invention, the “pure” natural dye(s) iii) are present in composition B in a total amount ranging from 0.05% to 25% by weight relative to the total weight of the dye composition, in particular ranging from 0.1 % to 10% by weight relative to the total weight of the dye composition, preferentially from 0.5% to 5% by weight relative to the total weight of composition B.

As regards the extracts iii), the content in composition B containing the extract(s) per se is preferably between 0.1 % and 20% by weight, relative to the weight of composition B, more preferentially from 0.5% to 5% by weight.

Organic solvents:

Compositions A and/or B as defined previously may comprise one or more organic solvents. Examples of preferred organic solvents include C1-C4 lower alkanols, such as ethanol and isopropanol; polyols and polyol ethers such as 2-butoxyethanol, propylene glycol, propylene glycol monomethyl ether, diethylene glycol monoethyl ether and monomethyl ether,

hexylene glycol, and also aromatic alcohols, for instance benzyl alcohol or phenoxyethanol.

The organic solvents are present in proportions preferably of between 0.1 % and 20% by weight approximately and even more preferentially between 0.5% and 10% by weight approximately, relative to the total weight of the composition under consideration.

Oils

Compositions A and/or B as defined previously may comprise one or more identical or different oils.

The term "o/T means a "fatty substance" that is liquid at room temperature (25°C) and at atmospheric pressure (760 mmHg); the viscosity at 25°C is preferably less than 1200 cps and better still less than 500 cps (defined, for example, from the Newtonian plateau determined using an ARG2 rheometer from TA Instruments equipped with a spindle with cone-plate geometry 60 mm in diameter and with an angle of 2 degrees over a shear stress range of from 0.1 Pa to 100 Pa).

The term "fatty substance" means an organic compound that is insoluble in water at ordinary temperature (25°C) and at atmospheric pressure (760 mmHg) (solubility of less than 5%, preferably less than 1 % and even more preferentially less than 0.1 %). They bear in their structure at least one hydrocarbon-based chain comprising at least 6 carbon atoms or a sequence of at least two siloxane groups. In addition, the fatty substances are generally soluble in organic solvents under the same temperature and pressure conditions, for instance chloroform, dichloromethane, carbon tetrachloride, ethanol, benzene, toluene, tetrahydrofuran (THF), liquid petroleum jelly or decamethylcyclopentasiloxane.

The term "non-silicone o/T means an oil not containing any silicon (Si) atoms and the term "silicone o/ means an oil containing at least one silicon atom.

More particularly, the oils are chosen from non-silicone oils and in particular OQ-O-IQ hydrocarbons or hydrocarbons containing more than 16 carbon atoms and in particular alkanes; oils of animal origin; triglyceride oils of plant origin; essential oils; fluoro oils or glycerides of synthetic origin, fatty alcohols; fatty acid and/or fatty alcohol esters other than triglycerides, fatty acid amides and silicone oils.

Preferably, the oils are not oxyalkylenated or glycerolated ethers.

Preferably, the oils do not comprise any C2-C3 oxyalkylene units or any glycerolated units.

Preferably, the oils are not fatty acids which, in salified form, give water-soluble soaps.

The oils that may be used as second ingredient b) in composition A or B in accordance with the invention may be silicones.

The silicones may be volatile or non-volatile, cyclic, linear or branched silicones, which are unmodified or modified with organic groups, having a viscosity from 5x10 6 to 2.5 m2/s at 25°C, and preferably 1 x10 5 to 1 m2/s.

Preferably, the silicone is chosen from polydialkylsiloxanes, especially polydimethylsiloxanes (PDMSs), and organomodified polysiloxanes comprising at least one functional group chosen from poly(oxyalkylene) groups, amino groups and alkoxy groups.

Organopolysiloxanes are defined in greater detail in Walter Noll’s Chemistry and

Technology of Silicones (1968), Academic Press. They may be volatile or non-volatile.

When they are volatile, the silicones are more particularly chosen from those with a boiling point of between 60°C and 260°C, and even more particularly from:

(i) cyclic polydialkylsiloxanes comprising from 3 to 7 and preferably from 4 to 5 silicon atoms. These are, for example, octamethylcyclotetrasiloxane, sold especially under the name Volatile Silicone® 7207 by Union Carbide or Silbione® 70045 V2 by Rhodia, decamethylcyclopentasiloxane sold under the name Volatile Silicone® 7158 by Union Carbide, and Silbione® 70045 V5 by Rhodia, and mixtures thereof.

Mention may also be made of cyclocopolymers of the dimethylsiloxane/methylalkylsiloxane type, such as Volatile Silicone® FZ 3109 sold by Union Carbide, having the formula:

" ' " '

CH3 - CH 3

with D’ — Si - O— with D' : - Si - O—

CH3 C8H 17

Mention may also be made of mixtures of cyclic polydialkylsiloxanes with organosilicon compounds, such as the mixture of octamethylcyclotetrasiloxane and tetratrimethylsilylpentaerythritol (50/50) and the mixture of octamethylcyclotetrasiloxane and oxy-1 ,1’-bis(hexa-2,2,2’,2’,3,3’-trimethylsilyloxy)neopentane;

(ii) linear volatile polydialkylsiloxanes containing 2 to 9 silicon atoms and having a viscosity of less than or equal to 5x10 6 m2/s at 25°C. An example thereof is decamethyltetrasiloxane sold especially under the name SH 200 by Toray Silicone. Silicones belonging to this category are also described in the article published in Cosmetics and Toiletries, Vol. 91 , Jan. 76, pp. 27-32, Todd & Byers, "Volatile Silicone Fluids for Cosmetics".

Non-volatile polydialkylsiloxanes, polydialkylsiloxane gums and resins, polyorganosiloxanes modified with the above organofunctional groups, and mixtures thereof, are preferably used.

These silicones are more particularly chosen from polydialkylsiloxanes, among which mention may be made mainly of polydimethylsiloxanes bearing trimethylsilyl end groups. The viscosity of the silicones is measured at 25°C according to ASTM standard 445 Appendix C.

Among these polydialkylsiloxanes, mention may be made, in a non-limiting manner, of the following commercial products:

- the Silbione® oils of the 47 and 70 047 series or the Mirasil® oils sold by Rhodia, for instance the oil 70 047 V 500 000;

- the oils of the Mirasil® series sold by the company Rhodia;

- the oils of the 200 series from the company Dow Corning, such as DC200 with a viscosity of 60 000 mm2/s;

- the Viscasil® oils from General Electric and certain oils of the SF series (SF 96, SF 18) from General Electric.

Mention may also be made of polydimethylsiloxanes bearing dimethylsilanol end groups, known under the name dimethiconol (CTFA), such as the oils of the 48 series from the company Rhodia.

Compositions A and/or B as defined previously may comprise one or more oils, chosen from fatty alcohols, fatty acid amides and fatty acid esters in the form of oils.

It is recalled that, for the purposes of the invention, fatty alcohols, esters and acids more particularly bear at least one linear or branched, saturated or unsaturated hydrocarbon-based group comprising 6 to 30 carbon atoms, which is optionally substituted, in particular with one or more hydroxyl groups (in particular 1 to 4). If they are unsaturated, these compounds may comprise one to three conjugated or unconjugated carbon-carbon double bonds.

More precisely, these compounds may represent an ester of a C1-C10 alcohol and of a C6-C30 fatty acid such as R-C(0)-0-R' with R representing a linear or branched C6-C30 alkyl or linear or branched C6-C30 alkenyl group, comprising one or two unsaturations, and R representing a linear or branched C1-C10 alkyl group.

Preferentially, R represents a linear C10-C20 alkyl group and R' represents a C1-C6 alkyl group that is preferably branched, such as isopropyl myristate.

According to another advantageous variant, the ingredient ii) represents one or more amides of a C6-C30 fatty acid and of a primary or secondary, preferably primary, C1-C10 amine, such as those of formula R”-C(0)-N(Ra)-R”’ with R” representing a linear or branched C6-C30 alkyl or a linear or branched C6-C30 alkenyl group, comprising one or two unsaturations, which may be substituted with one or more hydroxyl groups, or (di)(Ci-C6)(alkyl)amino, and R’” representing a linear or branched C1-C10 alkyl group, Ra representing a hydrogen atom or an alkyl group as defined for R’”. Preferably, R” represents a C14-C20 alkenyl group, Ra represents a hydrogen atom and R’” represents a C1-C6 alkyl group optionally substituted with (di)(Ci-C4)(alkyl)amino such as oleylamidopropyldimethylamine.

As regards the C6-C16 alkanes, they are linear or branched, and possibly cyclic. Examples that may be mentioned include hexane, dodecane and isoparaffins such as isohexadecane and isodecane. The linear or branched hydrocarbons containing more than 16 carbon atoms may be chosen from liquid paraffins, petroleum jelly, liquid petroleum jelly, polydecenes, and hydrogenated polyisobutene such as Parleam®, squalane, squalene, and mixtures thereof.

Among the hydrocarbons, mention may be made of the refined vegetable perhydrosqualene sold under the name Fitoderm by the company Cognis; the vegetable squalane sold, for example, under the name Squalive by the company Biosynthis.

Mention may also be made of the following compounds:

- a mixture of C15-C16 branched alkanes, for example that which is sold by the company

SEPPIC under the name Emogreen L15;

- a mixture of C13-C15 linear and/or branched alkanes, for example that which is sold by the company SEPPIC under the name Emosmart L15.

Among the animal oils, mention may be made of perhydrosqualene.

Among the triglycerides of plant or synthetic origin, mention may be made of liquid fatty acid triglycerides containing from 6 to 30 carbon atoms, for instance heptanoic or octanoic acid triglycerides, or alternatively, for example, sunflower oil, corn oil, soybean oil, marrow oil, grapeseed oil, sesame oil, hazelnut oil, apricot oil, macadamia oil, arara oil, castor oil, avocado oil, caprylic/capric acid triglycerides, for instance those sold by the company Stearinerie Dubois or those sold under the names Miglyol® 810, 812 and 818 by the company Dynamit Nobel, jojoba oil and shea butter oil.

Among the fluoro oils, mention may be made of perfluoromethylcyclopentane and perfluoro-1 ,3-dimethylcyclohexane, sold under the names Flutec® PC1 and Flutec® PC3 by the company BNFL Fluorochemicals; perfluoro-1 ,2-dimethylcyclobutane; perfluoroalkanes such as dodecafluoropentane and tetradecafluorohexane, sold under the names PF 5050® and PF 5060® by the company 3M, or bromoperfluorooctyl sold under the name Foralkyl® by the company Atochem; nonafluoromethoxybutane and nonafluoroethoxyisobutane; perfluoromorpholine derivatives such as 4-(trifluoromethyl)perfluoromorpholine sold under the name PF 5052® by the company 3M.

Among the essential oils contained in the composition of the invention, mention may be made of those mentioned in Ullmann's Encyclopedia of Industrial Chemistry ("Flavors and Fragrances", Karl-Georg Fahlbusch et al., Published Online: 15 JAN 2003, DOI: 10.1002/14356007. a 1 1 _ 141 ).

Preferably, the oil(s) of the invention are non-silicone oils. The term "non-silicone o/ means an oil not containing any silicon (Si) atoms and the term "silicone o/T means an oil containing at least one silicon atom.

According to a variant of the invention, the oil(s) are chosen from OQ-O-IQ alkanes, hydrocarbons containing more than 16 carbon atoms, polydecenes, liquid esters of a fatty acid and/or of a fatty alcohol, and liquid fatty alcohols, or mixtures thereof.

Better still, the oils are chosen from liquid petroleum jelly, C6-C16 alkanes, polydecenes and hydrocarbons containing more than 16 carbon atoms.

In this preferred variant, the oil(s) are chosen from mineral oils such as liquid petroleum jelly, squalane and squalene.

According to another most particularly preferred mode of the invention, the oils are chosen from oils of natural origin, more particularly oils of plant origin, preferentially chosen from jojoba oil, babassu oil, sunflower oil, olive oil, coconut oil, Brazil nut oil, marula oil, corn oil, argan oil, soybean oil, marrow oil, grapeseed oil, linseed oil, sesame oil, hazelnut oil, apricot oil, macadamia oil, arara oil, coriander oil, almond oil, castor oil, avocado oil, shea butter oil and also rapeseed oil, borage oil, evening primrose oil, pomegranate oil, mango oil, palm oil, cottonseed oil and coconut kernel oil, and mixtures thereof.

More particularly, compositions A and/or B may contain one or more oils of plant origin preferably chosen from avocado oil, olive oil, coconut oil, coconut kernel oil, argan oil and sunflower oil; more preferentially, the oil(s) of the invention are chosen from coconut kernel oils, and mixtures thereof.

According to a preferred embodiment, compositions A and/or B may contain one or more oils chosen from C6-C16 hydrocarbons or hydrocarbons containing more than 16 carbon atoms, and in particular alkanes; preferably from:

C6-C16 hydrocarbons, the latter being linear, branched, and optionally cyclic, preferably chosen from hexane, dodecane, isoparaffins such as isohexadecane and isodecane, and mixtures thereof;

linear or branched hydrocarbons containing more than 16 carbon atoms, preferably chosen from liquid paraffins, petroleum jelly, liquid petroleum jelly, polydecenes, and hydrogenated polyisobutene such as Parleam®, hemisqualane, squalane and squalene, and mixtures thereof;

and mixtures thereof.

Compositions A and/or B used in the process of the invention preferably comprise one or more oils in an amount inclusively between 1 % and 80% by weight, more particularly between 2% and 50% by weight, preferentially between 3% and 40% by weight and more preferentially between 2% and 25% by weight, relative to the total weight of said compositions.

Adjuvants:

Compositions A and/or B used in the process of the invention may also contain various adjuvants conventionally used in hair dye compositions, such as anionic, cationic, amphoteric or nonionic surfactants, mineral or organic thickeners, and in particular anionic, cationic, nonionic and amphoteric polymeric associative thickeners, antioxidants, penetrants, sequestrants, fragrances, buffers, dispersants, conditioning agents, for instance ceramides, film-forming agents, preserving agents, opacifiers and mineral or organic thickeners such as clays.

The above adjuvants are generally present in an amount for each of them of between 0.01 % and 40% by weight relative to the weight of the composition, and preferably between 0.1 % and 20% by weight relative to the weight of the composition under consideration.

Needless to say, a person skilled in the art will take care to select this or these optional additional compound(s) such that the advantageous properties intrinsically associated with the composition or the poultice that are useful in the dyeing process in accordance with the invention are not, or are not substantially, adversely affected by the envisaged addition(s).

Additional dyes:

Compositions A and/or B used in the dyeing process of the invention may also contain one or more additional direct dyes, in particular synthetic dyes or dyes of natural origin, other than the indigo-producing plant powder and/or extract i) and the henna ii) and the natural dyes iii) as described previously.

The synthetic direct dyes are preferably chosen from those conventionally used in direct dyeing, among which may be mentioned all the commonly used aromatic and/or non-aromatic dyes, such as neutral, acidic or cationic nitrobenzene direct dyes, neutral, acidic or cationic azo direct dyes, natural direct dyes, neutral, acidic or cationic quinone and in particular anthraquinone direct dyes, azine, triarylmethane or indoamine direct dyes, methines, styryls, porphyrins, metalloporphyrins, phthalocyanines, methine cyanines and fluorescent dyes.

Preferentially, the natural direct dyes other than indigo i) and henna ii) are chosen from condensed, gallic or ellagic tannins, naphthoquinones (juglone, lawsone), anthraquinones (emodin, alizarin, etc.), isatin, curcumin, spinulosin, polyphenols such as flavonoids, isoflavonoids, pterocarpans, neoflavones or orceins.

These natural dyes may be added in the form of defined compounds, extracts or plant parts. Said defined compounds from extracts or from plant parts are preferably in the form of powders, in particular fine powders whose particles have sizes identical to that of the indigo-producing plant powder as defined previously.

When it is (they are) present, the natural or synthetic direct dye(s) other than the indigo-producing plant powder i) and henna ii) used in the process of the invention particularly represent from 0.001 % to 10% by weight relative to the total weight of the ready-to-use composition and even more preferentially from 0.05% to 5% by weight relative to the total weight of the composition under consideration.

Preferably, the compositions of the invention do not contain any synthetic direct dyes, i.e. dyes that do not occur in nature.

Advantageously, composition B may comprise one or more additional natural dyes chosen from the compounds of formula (a) or (b) below, or mixtures thereof:

Such compounds are, for example, extracted from moulds of the species Monascus purpureus (synonyms: M. albidus, M. anka, M. araneosus, M. major, M. rubiginosus and M. nίhί)

Composition A used in the process of the invention may also comprise one or more oxidation bases and/or one or more couplers conventionally used for dyeing keratin fibres.

Among the oxidation bases, mention may be made of para-phenylenediamines, bis(phenyl)alkylenediamines, para-aminophenols, bis-para-aminophenols, ortho-aminophenols and heterocyclic bases, and the addition salts thereof.

Among these couplers, mention may be made especially of meta-phenylenediamines, meta-aminophenols, meta-diphenols, naphthalene-based couplers and heterocyclic couplers, and the addition salts thereof.

When it is (they are) present, the oxidation base(s) present in the composition(s) are each generally present in an amount of between 0.001 % and 10% by weight, of the total weight of the dye composition(s).

Preferably, the dyeing process of the invention does not use any oxidation dyes.

pH of the ready-to-use composition A

According to a particular mode of the invention, the pH of the ready-to-use composition A after mixing with the aqueous composition, preferably with water, containing the ingredients i) and optionally ii), ranges from 2 to 9, preferably from 3 to 7 and better still from 4 to 6.5.

The pH of the ready-to-use composition A may be adjusted to the desired value by means of acidic or alkaline agents usually used in the dyeing of keratin fibres, or alternatively using standard buffer systems.

Among the acidic agents that may be used in the compositions of the invention, mention may be made of mineral or organic acids, for instance hydrochloric acid, orthophosphoric acid or sulfuric acid, carboxylic acids, for instance acetic acid, tartaric acid, citric acid and lactic acid, and sulfonic acids; the acid is preferably an organic acid such as citric acid.

The surfactant(s)

According to a particular embodiment, the dyeing process uses one or more surfactants. Preferably, the surfactant(s) are chosen from anionic and nonionic surfactants.

Dyeing process according to the invention

The dyeing process according to the invention involves two different compositions A and B used during two different steps E1 ) and E2), via their application to keratin fibres.

According to a preferred process according to the invention, composition A is applied first to the keratin fibres; and composition B is applied to the keratin fibres after the application of composition A; the process preferably involves at least one rinsing step, and/or a washing step between the dyeing step involving composition A and the treatment step involving the application of composition B.

Preferably, the dyeing process according to the invention involves the following steps:

- the first step consists in preparing composition A as defined previously, in particular in the form of a poultice as defined previously comprising water, using indigo-producing plant powder and/or extract i) and optionally henna ii);

- the ready-to-use composition A as defined previously is then applied to the keratin fibres and is left on said fibres preferably for a minimum time of 10 minutes, preferentially a time ranging from 10 minutes to 12 hours, better still ranging from 15 to 75 minutes and better still from 15 to 60 minutes;

- said fibres are then treated with the aqueous composition B whose pH is less than 7 and comprising one or more natural dyes iii) chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betalains, preferably betanin;

iii-iii) anthocyanidins (also known as anthocyanides or anthocyanidols), preferably of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

iii-iv) carthamine;

iii-v) naphthoquinones comprising at least two hydroxyl groups, preferably at least three hydroxyl groups, preferably chosen from alkanine (also known as Orcanette) and/or shikokine;

and mixtures thereof;

and iv) one or more acidifying agents.

Preferably, between the step of applying the ready-to-use composition A and the step of applying composition B, the keratin fibres are rinsed with water until the poultice has disappeared, and/or washed in the presence of a shampoo; preferably, according to this third step, the fibres are rinsed with water without being shampooed;

- preferably, on conclusion of this rinsing and/or washing step, if said step is performed, the keratin fibres may then be either dried or left wet, preferably left wet.

According to another embodiment of the process according to the invention, composition B as defined previously is applied first to the keratin fibres, and the ready-to-use composition A as defined previously is then applied to the keratin fibres and is left to stand on said fibres preferably as defined previously. According to this embodiment, the fibres are also preferably rinsed as described previously.

Preferably, on conclusion of the dyeing process according to the invention, the keratin fibres are washed and/or rinsed.

The ready-to-use composition A preferably comprises water and is in the form of a poultice; it may also comprise one or more oils, and/or one or more organic solvents and cosmetic additives, mixed with the indigo-producing plant powder i) and optionally with the henna ii).

According to another embodiment of the invention, the indigo-producing plant powder i) and optionally the henna and is mixed with or crumbled into an aqueous composition, preferably water, at a temperature below 100°C, in particular between 25°C and 70°C and better still between 25°C and 50°C.

Preferably, the temperature of application of composition A ranges from room temperature (15°C to 25°C) to 50°C and more particularly from 25°C to 40°C.

After applying the poultice according to the invention, the head of hair may advantageously be subjected to a heat treatment by heating at a temperature ranging from 30°C to 150°C and better still from 30°C to 60°C. In practice, this operation may be performed using a hairstyling hood, a hairdryer, an infrared ray dispenser or any other standard heating appliance.

A particular embodiment of the invention relates to a dyeing process which is performed at room temperature (25° C).

The evaluation of the colouring obtained on the keratin fibres may be performed visually or with a spectrocolorimeter in the CIE L*a*b* system, for example using a Minolta CM 3600 spectrocolorimeter (illuminant D65, angle 10°, specular component included).

In this L*a*b* system, L* represents the lightness of the colour, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis. The smaller the value of L*, the darker and more powerful the colouring.

The smaller the value of a*, the greener the colour and the higher the value of a*, the redder the colour.

The smaller the value of b*, the bluer the colour and the higher the value of b*, the yellower the colour.

The colour buildup on the hair corresponds to the variation in colouring between the locks of hair before and after the treatment or dyeing are defined by (DE*) according to the following equation:

In this equation, L*, a* and b* represent the values measured on locks of hair after dyeing and Lo*, ao* and bo* represent the values measured on locks of undyed hair. The higher the DE* value, the better is the buildup of the colour.

The stability of the colouring of the keratin fibres over time, especially after 9 days, was also evaluated by measuring the colour coordinates of the keratin fibres and comparing them with the colour coordinates immediately after performing the dyeing process according to the invention. The colour difference DE* between the colour at TO and the colour after 9 days represents the stability of the colour of the hair and is calculated by means of the following equation:

In this equation, *, ao* and bo * represent the colorimetric coordinates measured on locks of hair at TO immediately after performing the process and l_3S*, a3s* and b*3S represent the colorimetric coordinates 9 days after performing the process. The smaller the value of AE*stab, the more stable the colouring.

In particular, in the context of the invention, a colouring for which the DE* 9 days after dyeing is less than 2 is considered as stable over time.

In the context of the present invention, it is thus sought to obtain, immediately after the dyeing process, a value of b* that is as small as possible and/or a value of a* that is as high as possible. It is sought to obtain these results while at the same time having efficient colour buildup (large colour buildup value) and colouring that is stable over time.

DYEING EXAMPLES

EXAMPLE 1 :

The following compositions were prepared:

The percentages are indicated on a weight basis relative to 100 g of composition.

1 . Dyeing step

The following dye composition is prepared by mixing, at the time of use, the natural dye powder with water at 50°C so as to make the following poultice:

The described ingredients i) and ii) are dissolved or dispersed in the relative amounts described in the above table in water at 50°C in a bowl. The whole is homogenized with a spoon or spatula.

The poultice obtained is very creamy, and is applied to locks of natural hair containing 90% white hairs, at a rate of 10 g of composition per 1 g of locks. The locks are left to stand for 60 minutes at 33°C under cellophane.

On conclusion of the leave-on time, the locks are rinsed and washed with Ultra Doux camomile shampoo, and then wrung dry.

2. Neutralizing post-treatment step

The following post-treatment compositions were prepared:

On conclusion of the dyeing step, the compositions are then applied at a rate of 5 g per gram of hair and left to stand on the hair for 15 minutes at 40°C under cellophane, comparatively with reference locks which have not undergone any post-treatment.

On conclusion of the leave-on time, all the locks are then rinsed and washed with Ultra Doux camomile shampoo, and then dried.

Colorimetric results

The colour of the locks was evaluated in the CIE L*a*b* system, using a Minolta CM 3600 spectrocolorimeter (illuminant D65, angle 10°, specular component included).

In this L*a*b* system, L* represents the intensity of the colour, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis.

The colour buildup corresponds to the variation in colouring between the locks of hair before and immediately after performing the process are defined by (DE*) according to the following equation:

In this equation, L*, a* and b* represent the values measured on locks of hair after dyeing and l_o*, ao* and bo* represent the values measured on locks of undyed hair. The higher the DE* value, the better is the buildup of the colour.

Colorimetric measurements were taken immediately after performing the process (TO) and then after 9 days (T 9D).

The colour difference DE between the colour at TO and the colour after 3 weeks represents the stability of the colour of the hair and is calculated by means of the following equation:

In this equation, Lo*, ao* and bo * represent the colorimetric coordinates measured on locks of hair at TO immediately after performing the process and l_9D*, ago* and b*9D represent the colorimetric coordinates 9 days after performing the process.

Delta b represents the variation between bo and b3S.

We observed that the colourings obtained with the processes according to the invention, involving a post-treatment with compositions B2 and B3, have no yellow/green tints.

Specifically, the dyeing process according to the invention involving a post-treatment with compositions B2 and B3 makes it possible to neutralize the unaesthetic yellow/green colour on the day of dyeing, in contrast with the comparative treatments of the invention without post-treatment or else with post-treatment compositions B1 (comparative 1 and 2).

This is reflected:

by markedly higher values of a* (less green and thus more red) for the hair treated in post-treatment with compositions B2 and B3 (processes of the invention) relative to the hair dyed without post-treatment or else with the post-treatment B1 (comparative 1 and 2).

- Furthermore, the processes according to the invention involving a post-treatment composition according to the invention (compositions B2 and B3) make it possible to obtain colourings that show better colour buildup (higher DE).

Furthermore, markedly lower values of b* (less yellow) are also obtained for the colourings obtained with the post-treatment compositions B2 and B3 (processes of the invention) when compared with the hair dyed without post-treatment or else with the

post-treatments B1 (comparative 1 and 2).

Moreover, the colourings obtained with the process of the invention are stable over time (low DE T0/T 9D value), in contrast with the colourings without post-treatment (comparative 1 ) which require a certain amount of time to obtain an aesthetic colour (brown).

In conclusion, the post-treatments of the invention (compositions B2 and B3) make it possible to obtain colourings that show better colour buildup (higher DE) and more aesthetic brown (higher red components or lower yellow components) from the end of the dyeing process. These colourings are moreover stable over time (low ^ETQ days-to).

The process of the invention thus makes it possible to accelerate the revelation of the colouring using henna and indigo to obtain the final dyeing result from the day of application and to avoid unaesthetic intermediate tints, while at the same time obtaining better colour buildup.

EXAMPLE 2

1. Dyeing step: The following dye composition was prepared by mixing, at the time of use, the natural dye powders with water at 50°C so as to make the following poultice:

This mixture is applied to locks of permanent-waved Caucasian hair containing 90% white hairs (PWW) at a bath ratio of 10 g per 1 g of lock. The locks are left to stand for 60 minutes at 33°C under cellophane.

On conclusion of the leave-on time, the locks are rinsed and washed with Ultra Doux camomile shampoo, and then wrung dry.

2. Neutralizing dyeing post-treatment

The following post-treatment compositions were prepared:

On conclusion of the dyeing step, each of the post-treatment compositions is then applied at a rate of 5 g per gram of hair to locks dyed beforehand with composition C2 and left to stand on the locks for 15 minutes at 33°C under cellophane, compared with reference locks dyed with composition C2 to which no post-treatment composition was applied.

On conclusion of the leave-on time, all the locks are then rinsed and washed with Ultra Doux camomile shampoo, and then dried.

Results:

The locks were evaluated visually and in the CIELab system as described previously.

We observed that:

Without an applied post-treatment, the poultice colours the hair in an unaesthetic golden green. Over time, the colouring changes and the green tint disappears, but the colouring retains an unaesthetic shade.

The basic post-treatment with dye (comparative composition B4) partially neutralizes the green of the colouring, but the shade remains unaesthetic.

The acidic post-treatment of the invention with the carminic acid dye according to the invention (composition B5) makes it possible to intensify the colour in terms of colour buildup and power and to neutralize the unaesthetic green/golden tint, in contrast with the comparative dyeing processes (without post-treatment or else with an alkaline post- treatment with dye).

These observations are confirmed by the colorimetric measurements, in particular with markedly lower values of b* (less yellow) for the hair treated with composition C2 followed by a post-treatment with composition B5 (process of the invention) relative to the hair dyed without post-treatment or else with the alkaline post-treatment C

(comparative 1 and 2).

Furthermore, the colorimetric values measured demonstrate, in the case of the post- treatment with composition B5 according to the invention, significantly higher values of DE* (better colour buildup) and lower values of L* (more intense colouring).

> Colour change over time:

Visual evaluation: After 3 weeks, in the case of the comparative processes 1 and 2, we observed that the colouring changes over time, and in particular that the green component of the colouring disappears. On the other hand, in the case of the dyeing via the process according to the invention, the colour is more stable than in the case of the comparative processes.

Colorimetric evaluation of the change in colouring:

The values of DE T3weeks/T0 and Db* T3weeks/T0 were calculated using the same equation as that described previously, but using the colorimetric values measured three weeks after performing the dyeing process.

This is confirmed by the colorimetric measurements with lower values of variation of the yellow/blue component (Db*) in the case of the treatments with the compositions of the invention and colour variations that were also lower (DE*).

Consequently, the dyeing process according to the invention makes it possible to stabilize the colouring from the day of application and in an aesthetic manner (less yellow/green) and more efficiently than via the comparative processes.

EXAMPLE 3

1 . Dyeing step: The following dye composition was prepared by mixing, at the time of use, the natural dye powders with water at 50°C so as to make the following poultice:

This poultice is applied to locks of permanent-waved hair (PWW) containing 90% white hairs at a bath ratio of 10g per 1 g of lock. The locks are left to stand for 45 minutes at 33°C under cellophane.

On conclusion of the leave-on time, the locks are rinsed and washed with Ultra Doux Camomile shampoo, and then wrung dry.

2. Neutralizing post-treatment step

On conclusion of the dyeing step, each of the post-treatment compositions B6 to B9 is then applied at a rate of 5 g per gram of hair to locks dyed beforehand with composition C3 and left to stand on the locks for 15 minutes at 40°C under cellophane, compared

with reference locks dyed with composition C3 to which no post-treatment composition was applied.

On conclusion of the leave-on time, all the locks are then rinsed and wrung dry, and then dried.

Results:

The colour of the locks was evaluated in the CIE L*a*b* system, using a Minolta CM 3600 spectrocolori meter (illuminant D65, angle 10°, specular component included).

In this L*a*b* system, L* represents the intensity of the colour, a* indicates the green/red colour axis and b* indicates the blue/yellow colour axis.

The colour buildup corresponds to the variation in colouring between the locks of hair before and immediately after performing the process are defined by (DE*) according to the following equation:

In this equation, L*, a* and b* represent the values measured on locks of hair after dyeing and L0*, aO* and bO* represent the values measured on locks of undyed hair. The higher the DE* value, the better is the buildup of the colour.

Whatever the family of natural dye used, it is found that the locks treated by the method according to the invention have a better colour buildup (values of dE* higher) and a more powerful color (value of L* lower) compared to the locks treated with the method without post-treatment (comparative 1 ).

In addition, the measured colorimetric values demonstrate a neutralization of the unsightly green / golden reflection (yellow component b* smaller) in the case of the locks treated with the method with a post-treatment according to the invention compared to the method without post-treatment (comparative 1 ).

CLAIMS

1. Process for dyeing keratin fibres, in particular human keratin fibres such as the hair, in which said fibres are treated in several steps, comprising:

at least one step E1 ) of dyeing said fibres using a cosmetic dye composition A comprising indigo-producing plant powder and/or indigo-producing plant dye extract i) and optionally henna ii);

at least one step E2) of treating said fibres using an aqueous cosmetic composition B whose pH is less than 7, comprising one or more natural dyes iii) chosen from:

o iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D and/or kermesic acid;

o iii-ii) betalains, preferably betanin;

o iii-iii) anthocyanidins (also known as anthocyanides, or anthocyanidols) preferably comprising at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

o iii-iv) carthamine;

o iii-v) naphthoquinones comprising at least two hydroxyl groups, preferably at least three hydroxyl groups, preferably chosen from alkanine (also known as Orcanette) and/or shikokine;

o and mixtures thereof;

iv) one or more acidifying agents,

it being understood that, preferably, composition A is applied first to the keratin fibres; and that composition B is applied to the keratin fibres after the application of composition A;

the process preferably involving at least one rinsing step and/or one washing step between the dyeing step using composition A and the treatment step involving the application of composition B.

2. Process according to the preceding claim, in which the indigo-producing plant(s) are chosen from the species of the following genera:

- Indigofera such as Indigofera tinctoria, Indigo suffruticosa, Indigofera articulata, Indigofera arrecta, Indigofera gerardiana, Indigofera argenta, Indigofera indica or Indigofera longiracemosa,

- Isatis such as Isatis tinctoria;

- Polygonum or Persicaria such as Polygonum tinctorium or Persicaria tinctoria ;

- Wrightia such as Wrightia tinctoria ;

- Calanthe such as Calanthe veratrifolia ; and

- Baphicacanthus such as Baphicacanthus cusia.

3. Process according to either of the preceding claims, in which the indigo-producing plant(s) are of the genus Indigofera and is more particularly Indigofera tinctoria.

4. Process according to any one of the preceding claims, in which composition A comprises a content of indigo-producing plant powder ranging from 10% to 99% by weight, relative to the total weight of composition A, more particularly ranging from 20% to 90% by weight and preferentially ranging from 40% to 80% by weight relative to the total weight of said composition A, when composition A is anhydrous.

5. Process according to any one of the preceding claims, characterized in that composition A comprises henna ii).

6. Process according to the preceding claim, characterized in that the henna is red henna.

7. Process according to either of Claims 5 and 6, characterized in that composition A used in the dyeing process comprises a content of henna ranging from 5% to 99% by weight, relative to the total weight of composition A, more particularly ranging from 10% to 60% by weight and preferentially ranging from 15% to 40% by weight relative to the total weight of said composition A, when composition A is anhydrous.

8. Process according to any one of Claims 1 to 3, 5 and 6, in which composition A comprises water, preferably comprises a water content ranging from 10% to 99% by weight, more particularly from 20% to 98% by weight and better still from 40% to 95% by weight relative to the weight of composition A.

9. Process according to the preceding claim, in which composition A comprises a content of indigo-producing plant powder and/or extract ranging from 0.5% to 50% by weight, more particularly ranging from 1 % to 40% by weight and preferentially ranging from 5% to 30% by weight, composition A comprising water.

10. Process according to any one of Claims 5, 6, 8 and 9, characterized in that composition A used in the dyeing process comprises a content of henna ranging from 0.1 % to 30% by weight, more particularly ranging from 0.15% to 20% by weight and preferentially ranging from 0.2% to 10% by weight relative to the total weight of composition A, composition A comprising water.

11. Process according to any one of Claims 5 to 10, characterized in that ingredients i) and ii) are present in composition A in a i/ii) weight ratio ranging from 0.1 to 95, preferably from 0.5 to 50 and better still from 1 to 10.

12. Dyeing process according to any one of the preceding claims, characterized in that composition A comprises one or more organic solvents preferably in a total content ranging from 0.2% to 35% by weight, preferably from 0.5% to 20% by weight and better still from 0.5% to 10% by weight relative to the total weight of composition A, preferably chosen from C1-C4 lower alkanols, such as ethanol and isopropanol; polyols and polyol ethers such as 2-butoxyethanol, propylene glycol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether and monoethyl ether, and hexylene glycol, and also aromatic alcohols such as benzyl alcohol or phenoxyethanol, and mixtures thereof.

13. Process according to any one of the preceding claims, in which the pH of composition A ranges from 2 to 9, preferably from 3 to 7 and better still from 4 to 6.5.

14. Process according to any one of the preceding claims, characterized in that composition B has a pH of less than 6 and preferably less than 5.

15. Process according to any one of the preceding claims, characterized in that composition B has a pH inclusively between 0.5 and 5, more particularly between 0.5 and 4.5 and preferably between 1 and 4.

16. Process according to any one of the preceding claims, characterized in that composition B comprises at least one acidifying agent chosen from organic and inorganic acids.

17. Process according to any one of the preceding claims, characterized in that the acidifying agent is chosen from hydrochloric acid, orthophosphoric acid, sulfuric acid, carboxylic acids chosen from acetic acid and citric acid; and mixtures thereof.

18. Process according to any one of the preceding claims, characterized in that the acidifying agent(s) represent from 0.001 % to 10% by weight relative to the weight of composition B and more particularly from 0.005% to 8% by weight relative to the weight of composition B.

19. Process according to any one of the preceding claims, characterized in that the natural dye(s) of composition B have an absorption wavelength max of between 625 and 750 nm or between 300 and 470 nm, better still between 625 and 750 nm.

20. Process according to any one of the preceding claims, characterized in that the natural dye(s) of composition B are present in a content of between 0.05% and 25% by weight relative to the total weight of the dye composition, in particular ranging from 0.1 % to 10% by weight relative to the total weight of the dye composition, preferentially from 0.5% to 5% by weight relative to the total weight of composition B.

21. Process according to any one of the preceding claims, characterized in that the natural dye(s) iii) of composition B are polyphenols chosen from:

iii-i) anthraquinones comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betalains, preferably betanin;

iii-iii) anthocyanidins (also known as anthocyanides or anthocyanidols), preferably of formula (Vg) which include at least three hydroxyl groups, preferably chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof;

iii-iv) carthamine;

and mixtures thereof.

22. Process according to any one of the preceding claims, characterized in that the natural dye(s) iii) of composition B comprise at least one carboxylic acid function, and are chosen from:

iii-i) anthraquinones, preferably comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D, pseudopurpurin, munjistin and/or kermesic acid;

iii-ii) betalains, preferably betanin;

iii-iv) carthamine.

23. Process according to any one of the preceding claims, characterized in that the natural dye(s) iii) of composition B are chosen from anthraquinones, comprising at least one carboxylic acid function, chosen from those of formula (A1 ) below:

and also the tautomeric and/or mesomeric forms thereof, the stereoisomers thereof, the addition salts thereof with a cosmetically acceptable acid or base, and the solvates thereof such as hydrates;

in which formula (A1):

• R1 and R8, which may be identical or different, represent a hydrogen atom, a hydroxyl group or an alkyl group such as methyl;

• R2 represents a hydrogen atom or a hydroxyl group, carboxyl group -C(0)0H or carboxylate group -C(0)0 , Q+ with Q+ representing an alkali metal or alkaline-earth metal such as potassium or calcium;

• R3 represents i) a hydrogen atom, ii) a hydroxyl group or iii) an optionally substituted aryl group, preferably a phenyl group optionally substituted with one or more groups chosen from a) hydroxyl, b) amino, c) (Ci-C6)alkyl optionally substituted with one or more groups chosen from hydroxyl, carboxyl and (Ci-C4)alkylcarbonylamino;

• R4 represents a hydrogen atom or a hydroxyl group;

• R5 represents a hydrogen atom, or a hydroxyl, carboxyl or carboxylate group -C(0)0-, Q+ with as defined previously;

• R6 represents a hydrogen atom, a hydroxyl group, -O , Q+ with Q+ as defined previously, carboxyl or carboxylate group -C(0)0 , Q+with Q+ as defined previously;

• R7 represents a hydrogen atom, a hydroxyl group or a glycosyl radical, preferably glucose;

• with the proviso that at least one from among R2, R5 and/or R6 represents a carboxyl group -C(0)0H or carboxylate group -C(0)0 , Q+ with Q+ representing an alkali metal or alkaline-earth metal such as potassium or calcium.

24. Process according to any one of the preceding claims, characterized in that the natural dye(s) iii) of composition B are chosen from anthraquinones comprising at least one carboxylic acid function, preferably chosen from carminic acid, laccaic acid A, laccaic acid B, laccaic acid C, laccaic acid D and/or kermesic acid.

25. Process according to any one of Claims 1 to 22, characterized in that the natural dye(s) of composition B are chosen from betalains, preferably betanin.

26. Process according to any one of Claims 1 to 21 , characterized in that the natural dye(s) of composition B are chosen from anthocyanidins (also known as anthocyanides, or anthocyanidols) of formula (Vg) below which include at least three hydroxyl groups:

in which formula (Vg):

• R1, R2, R3, R4, R10, R11, R12, R13 and R14, which may be identical or different, represent a hydrogen or halogen atom or a group chosen from i) hydroxyl, ii) (Ci-C6)alkyl, iii) (Ci-C6)alkoxy, iv) (Ci-C6)alkylthio, v) carboxyl, vi) alkyl or alkoxycarbonyl carboxylate, vii) optionally substituted amino, viii) optionally substituted linear or branched alkenyl, ix) optionally substituted cycloalkyl, x) optionally substituted aryl, xi) a group containing one or more silicon atoms, xii) (di)((hydroxy)(Ci-C6)alkyl)amino, xiii) glucosyl, xiv) R-Z-C(X)-Y- with R representing a hydrogen atom or a (Ci-Ce)alkyl or aryl group that is optionally substituted, especially with at least one hydroxyl group, such as 3,4,5-trihydroxyphenyl; Y and Z, which may be identical or different, represent a bond or an oxygen or sulfur atom or a group -N(R’)-with R’ representing a hydrogen atom or a (Ci-Ce)alkyl group, Y also possibly representing a (Ci-C6)alkylene group; X representing an oxygen or sulfur atom or N-R” with R” representing a hydrogen atom or a (Ci-C6)alkyl group;

• R6 and R8, which may be identical or different, represent a hydrogen atom or a group chosen from a hydroxyl group, a (Ci-C6)alkyl group or a group R-Z-C(X)-Y- as defined previously;

• or alternatively the unit (V) constitutes the polymeric unit of a polyphenol which will be linked to the other units of said polyphenol via positions 4, 6 or 8 of the chroman ring, in which case R1, or R3 and R6 form a covalent bond with the other units of said polyphenol;

it being understood that at least three radicals of the compounds of formula (V) chosen from R1, R2, R3, R4, R8, R10, R11, R12, R13 and R14 represent a hydroxyl group;

the compound of formula (Vg) being cationic and is associated with an organic or mineral anionic counterion An , such as halide,

preferably, the radicals R1 , R6, R14 and R10 representing a hydrogen atom.

27. Process according to any one of Claims 1 to 21 and 26, in which said natural dye(s) iii) are chosen from anthocyanidins chosen from cyanidin, delphinidin, pelargonin, malvidin, peonidin and petunidin, and mixtures thereof.

28. Dyeing process according to any one of Claims 1 to 22, characterized in that said natural dye(s) iii) are chosen from carthamine.

29. Dyeing process according to any one of the preceding claims, characterized in that composition A is applied first to the keratin fibres; and composition B is applied to the keratin fibres after the application of composition A.

30. Dyeing process according to any one of the preceding claims, characterized in that it involves at least one rinsing step, and/or one washing step between the dyeing step involving composition A and the treatment step involving composition B, preferably a rinsing step.

31. Use of an aqueous composition B whose pH is less than 7, comprising one or more acidifying agents iv) as defined according to any one of the preceding claims and one or more natural dyes iii) as defined according to any one of the preceding claims, for accelerating the stabilization over time of the colour of the fibres dyed with indigo-producing plant powder and/or extract and optionally henna and for improving the colour intensity and/or the colour buildup and/or the colour persistence.