Use for coloring the keratin fibers of at least one compound selected from the leuco-type compounds of the formula (I), the azometin-type dyes with pyrazolopyridine unit of the formula (II), which correspond to the compounds of the formula (I), its mesomeric, isomeric and tautomeric forms, as well as its addition salts with an acid and its solvates: ** Formula ** in which: * Z1 represents an oxygen atom, an NR6 group, when Z1 represents NR6 then R1 and R6 can form, together with the nitrogen atom to which they are attached, a saturated, unsaturated or aromatic heterocycle, of 5 to 8 members, optionally substituted, Z1 can also represent a divalent radical S, SO, SO2 when R1 is a methyl radical, * R1 and R6 independently represent: - a hydrogen atom, - an optionally substituted C1-C10 alkyl radical, the substituent may eventually be a saturated, unsaturated or aromatic (hetero) cycle co of 5 to 8 members, optionally substituted, - a saturated, unsaturated or aromatic 5 to 8 membered (hetero) cycle, optionally substituted, * R2, R3, R4, R5, independently, represent: - a hydrogen atom, - an optionally substituted C1-C4 alkyl radical, - a group selected from NH2, NHR10, NR11R12, OH, OR9, with R9 and R10 representing a linear or branched C1-C6 alkyl, optionally substituted, identical or different R11 and R12 represent a linear or branched C1-C6 alkyl, optionally substituted, with R11 and R12 being able to form together with the nitrogen atom to which they are attached, a saturated, unsaturated, or aromatic heterocycle of 5 to 8 members which optionally contains one or more others heteroatoms or groups selected from N, O, S, SO2, CO, the heterocycle being optionally substituted, * R2, R3, R4, R5, can form a saturated or unsaturated (hetero) cycle, two or two adjacent adjacent ones, possibly replaced, * n it is an integer between 0 and 3； * U represents CR or N； * R represents - a hydrogen atom, - a C1-C4 alkyl radical optionally substituted with a hydroxyl radical； - a C1
