Keratin fibers are colored by an agent comprising a coupler which is a m-phenylenediamine derivative of the formula (I) ##STR00001## wherein R.sup.1 is a C.sub.1 C.sub.4 alkyl group or a C.sub.1 C.sub.4 monohydroxyalkyl group; R.sup.2 is a methyl or an ethyl group; each of R.sup.3 and R.sup.4 is independently a branched or unbranched C.sub.2 C.sub.6 hydroxyalkyl group; and a cosmetically acceptable carrier. These couplers exhibit improved toxicological and dermatological properties and permit hair colorations in a broad color spectrum with good fastness properties.