Azomethine compound of formula below, organic or mineral acid salts thereof, tautomeric forms, optical isomers or geometrical isomers thereof and solvates thereof: in which formula: • n represents an integer equal to 0, 1, 2, 3 or 4, • R represents: - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more identical or different radicals chosen from hydroxyl or imidazolium radicals, An -; An - denoting a cosmetically acceptable anion or mixture of anions, - a C 1 -C 4 alkoxy radical, - a halogen atom, • R 1 represents: - a linear or branched C 2 -C 8 alkyl radical, optionally substituted with one or more hydroxyl radicals, • R 2 and R 3 represent, independently of each other: - a hydrogen atom, - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more hydroxyl radicals, • R 2 and R 3 may form, together with the nitrogen atom to which they are attached, a pyrrolidino, piperidino or morpholino ring, • X represents: - a hydroxyl radical, - a radical -NR 4 R 5 in which R 4 and R 5 represent, independently of each other: - a hydrogen atom, - a linear or branched C 1 -C 6 alkyl radical, optionally substituted with one or more hydroxyl or C 1 -C 4 alcoxy radicals, it being understood that the compounds of formula cannot represent the following compounds or: • n represents an integer equal to 0, 1, 2, 3 or 4, • R represents: - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more identical or different radicals chosen from hydroxyl or imidazolium radicals, An -; An - denoting a cosmetically acceptable anion or mixture of anions, - a C 1 -C 4 alkoxy radical, - a halogen atom, - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more identical or different radicals chosen from hydroxyl or imidazolium radicals, An -; An - denoting a cosmetically acceptable anion or mixture of anions, - a C 1 -C 4 alkoxy radical, - a halogen atom, • R 1 represents: - a linear or branched C 2 -C 8 alkyl radical, optionally substituted with one or more hydroxyl radicals, - a linear or branched C 2 -C 8 alkyl radical, optionally substituted with one or more hydroxyl radicals, • R 2 and R 3 represent, independently of each other: - a hydrogen atom, - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more hydroxyl radicals, - a hydrogen atom, - a linear or branched C 1 -C 4 alkyl radical, optionally substituted with one or more hydroxyl radicals, • R 2 and R 3 may form, together with the nitrogen atom to which they are attached, a pyrrolidino, piperidino or morpholino ring, • X represents: - a hydroxyl radical, - a radical -NR 4 R 5 in which R 4 and R 5 represent, independently of each other: - a hydrogen atom, - a linear or branched C 1 -C 6 alkyl radical, optionally substituted with one or more hydroxyl or C 1 -C 4 alcoxy radicals, - a hydroxyl radical, - a radical -NR 4 R 5 in which R 4 and R 5 represent, independently of each other: - a hydrogen atom, - a linear or branched C 1 -C 6 alkyl radical, optionally substituted with one or more hydroxyl or C 1 -C 4 alcoxy radicals, - a hydrogen atom, - a linear or branched C 1 -C 6 alkyl radical, optionally substituted with one or more hydroxyl or C 1 -C 4 alcoxy radicals,