The invention relates to the utilization of onium aldehydes and onium ketones of formula (1) or the derivatives thereof. In the formula, R1 represents a hydrogen atom, a (C1-C4)-alkyl group, an aryl group or a heteroaryl group. R2, R3, R4, independent of one another, each represent a hydrogen atom, a halogen atom, a (C1-C4)-alkyl group, a (C1-C4)-alkoxyl group, hydroxy-(C1-C4)-alkoxyl group, hydroxyl group, nitro group, aryl group, trifluoromethyl group, amino group or (C1-C4)-acyl group. Said amino group can be substituted by (C1-C4)-alkyl groups. Two of the residuals can be combined to form a fused benzene ring. R5 represents a (C1-C4)-alkyl group, aryl group, alkylaryl group or heteroaryl group. X designates a direct bonding or an optionally substituted vinyl group or phenyl group and Y— represents halogenide, benzenesulfonate, p-toluenesulfonate, methane sulfonate, trifluoromethane sulfonate, perchlorate, sulfate, hydrogen sulfate, tetrachlorozincate or N-oxide of the heterocyclic compound. In order to dye fibers containing keratin, onium aldehydes and onium ketones or the derivatives thereof are utilized in combination with at least one compound with a primary or secondary amino group or hydroxyl group. The compound is selected from primary or secondary aliphatic or aromatic amines, heterocyclic compounds containing nitrogen, amino acids, oligopeptides, said oligopeptides containing from 2 to 9 amino acids, as well as aromatic hydroxy compounds, and/or at least one CH-active compound.