It is however, usually preferable that the alkali-soluble dye is an azo compound having at least one phenolic hydroxy group in a molecule selected from the class consisting of the compounds represented by either one of the general formulas ##STR2## in which R5 is a hydrogen atom or a hydroxy group and R6 is a hydrogen atom, nitro group or a di(lower alkyl)amino group, the lower alkyl group having,