A group of particularly suitable black anionic dyes is that of formula ##STR1## wherein one X is hydroxy and the other X is amino or hydrogen, A is an unsubstituted or a substituted phenyl or naphthyl radical, B is a phenyl or naphthyl radical containing at least one amino and/or hydroxyl group as well as further optional substituents, Z is a radical of formula ##STR2## and R and R' are each indep