The invention relates to the use of a compound of formula (I) below, addition salts thereof, optical isomers, geometrical isomers and tautomers thereof and/or solvates thereof: Formula (I) in which: • R represents a hydrogen atom or a C1-C4 alkyl or C1-C4 hydroxyalkyl radical, preferably a hydrogen atom, • R2, R3, R4 and R5 independently represent: —a hydrogen atom, —a linear C1-C4 or branched C3-C4 alkyl radical, optionally substituted with a hydroxyl radical, • R1 represents a linear C2-C10 or branched C3-C10 alkyl radical, optionally interrupted with one or more heteroatoms chosen from O or S or with one or more groups —NR′, said alkyl radical ending with a group —NX1X2 or —OX3 or a radical chosen from: Formula (II) —X1 and X2 independently denote ◯ a hydrogen atom ◯ a linear C1-C6 alkyl radical or a branched C3-C6 alkyl radical ◯ a linear C1-C6 hydroxyalkyl radical or a branched C3-C6 hydroxyalkyl radical, X1 and X2 may form, with the nitrogen atom that bears them, a saturated or unsaturated 5- to 8-membered heterocycle, in which one of the ring members may be a heteroatom chosen from O, S and N said heterocycle possibly being substituted with one or more linear or branched C1-C4 alkyl, C1-C4 hydroxyalkyl or dimethylamino radicals, —X3 denotes a hydrogen atom or a linear C1-C6 or branched C3-C6 alkyl radical, —R′ denotes a hydrogen atom or a linear C1-C4 or branched C3-C4 alkyl radical, for dyeing keratin fibres, especially human keratin fibres such as the hair.
