Although the development of the color pattern on the integument, that is the skin, of mammals occurs towards the end of embryogenesis, we suggest that it reflects an underlying pre-pattern that is laid down much earlier. In mammals the pre-pattern is formed in the early stages of embryonic development. To create the color patterns certain genetically determined cells, called melanoblasts, migrate over the surface of the embryo and become specialized pigment cells, called melanocytes, which lie in the basal layer of the epidermis.