The present disclosure relates to methods for improving the quality and durability of color in artificially colored hair. The methods employ alkaline earth metal salts that act as a mordant (a fixing agent) with the dye and hydroxy-polycarboxylic acids, which act as chelators. The artificially colored hair is treated with a post-color treatment composition comprising one or more alkaline earth metal salts and one or more hydroxy-polycarboxylic acids. Also, the one or more alkaline earth metal salts may be incorporated into a coloring composition for coloring the hair (in-color treatment composition) and a subsequent post-color treatment composition comprising one or more hydroxy-polycarboxylic acids can be applied to the hair.