The invention relates to a method for dyeing human keratin fibres, comprising the application of a composition containing, in a cosmetically suitable medium, a vegetable extract including at least one compound having formula (I) as a dye precursor, or the addition salts thereof, combined with an external stimulus, selected from a heat, light or chemical stimulus produced using one or more organic and/or inorganic salts, in which formulae: R1 represents a hydrogen, a methyl, a hydroxymethyl, an aldehyde, -CO2R4 with R4 representing a hydrogen or an alkyl at C1-C2, a sugar radical； R2 represents a hydrogen, a hydroxyl, a sugar radical； R3, identical or non-identical, represent a hydrogen, a hydroxyl, an alkyl(C1-C4)oxy, the hydroxyl group number not exceeding 2； R represents a sugar radical； n is an integer between 1 and 5； the sugar radical originating from an aldose or an aldose derivative； the compounds having formula (I) having undergone, either prior to or simultaneously with the dyeing method, a step consisting in replacing radical R with a hydrogen atom.
