In order to improve the wash-resistance of hair dyes, in particular hair dyes applied on hair which has been already previously damaged, the dyed hair is treated with an aqueous protein composition that contains a dissolved protein, a protein hydrolysate or their water-soluble alkaline salts or alkaline earth salts, preferably an alkaline or alkaline earth caseinate. An aqueous metallic salt composition that forms water-insoluble deposits together with the protein composition is then applied on the hair.
