Skin colour

This depends on three factors.

Colour of skin itself, yellow due to presence of carotene.

Blood, showing through from vascular dermis, imparting a reddish hue.

The presence of varying amounts of melanin pigment responsible for shades of brown. Melanin is present mainly in the stratum germinative layer and deeper parts of the spiny layer. As cells move to the surface the granules of melanin become dust-like and cannot be identified.

In coloured races, pigment is present in greater amounts in all layers of the epidermis. The melanin comes from special cells, melanocytes (black cells), which then distribute it to the epidermal cells.

Exposure to x-rays and to ultraviolet light increases the enzymic activity of these cells and thus leads to increased melanin production and deposition in the epidermis, tanning.