The object of the invention is an agent for coloring fibers, which contains at least one aromatic aldehyde compound, at least one compound of formula (I) or (II) and an alkanolamine, in which R1 represents a C1 to C3 alkyl group, a C1 to C3 alkoxyalkyl group or a C1 to C3 hydroxyalkyl group and R2 represents hydrogen or a hydroxy group, a methoxy group, a halogen atom, an amino group or a dimethylamino group and A− represents an anion, such as chloride, bromide, sulfate, hydrogen sulfate, monomethyl sulfate, acetate, lactate or iodide; a method for coloring fibers using this agent, as well as a multicomponent kit for coloring and, later on, decolorizing fibers.