Method for dyeing keratinous fibres using 4-hydroxyindole derivatives at acid pH and compositions used

Agent for dyeing keratinous fibres, which comprise at least two components:

• a component (A) consisting of a composition containing, in a medium appropriate for dyeing, 0.01 to 4% by weight, relative to the total weight of the component (A), of an indole coupler corresponding to the formula:
• ##STR6## in which R.sub.1 denotes a hydrogen atom or a C.sub.1 -C.sub.4 alkyl radical;
• R.sub.2 and R.sub.3, which may be identical or different, denote a hydrogen atom, a C.sub.1 -C.sub.4 alkyl radical, a carboxyl radical or an alkoxycarbonyl radical;
• and X denotes a hydrogen atom, a C.sub.1 -C.sub.4 alkyl radical, a C.sub.1 -C.sub.18 alkoxy radical, a halogen atom or an acetylamino group;
• at least one of the groups X, R.sub.1, R.sub.2 and R.sub.3 being other than hydrogen;
• or salts of these compounds and 0.05 to 7% by weight, relative to the total weight of component (A), of an oxidation dye precursor, and a component (B) consisting of a composition containing an oxidizing agent selected from the group consisting of hydrogen peroxide, urea peroxide, persulfates, perborates and alkali metal bromates in a medium appropriate for dyeing, the pH of the components (A) and (B) being such that, after mixing in proportions of 90 to 10% in respect of component (A) and of 10 to 90% in respect of component (B), the resulting composition has a pH of less than 7, said resulting composition being free of iodide and nitrite ions in an amount sufficient to oxidize said indole coupler and said oxidation dye precursor.