A method of coloring porous material, especially human hair, is described, which method comprises applying to the material being colored, in any desired order successively, or simultaneously, a) at least one capped diazonium compound and b) at least one cationic water-soluble aromatic coupling component, under conditions such that, initially, coupling does not take place, and then causing the capped diazonium compound present on the material to react with the coupling component.