1. A METHOD OF DYEING AND CHEMICALLY MODIFYING A KERATINOUS MATERIAL WHICH COMPRISES REACTING AND KERATINOUS MATERIAL IN A REDUCED STATE WITH A COMPOUND CONTAINING AN ACYL-NITROGEN GROUP LINKED THROUGH THE NITROGEN TO AN AROMATIC GROUP, THE ACYL RADICAL CONTAINING AN OLEFIN DOUBLE BOND BETWEEN TWO CARBON ATOMS ONE OF WHICH IS DIRECTLY LINKED TO THE NON-OXO CARBONYL GROUP OF SAID ACYL-NITROGEN GROUP, AND WHEREIN THE AROMATIC GROUP CONTAINS A CHROMOPHORE GROUP SELECED FROM THE CLASS CONSISTING OF AZO, NITROSO, AZOXY, NITRO, AND AZOMETHINE.