What accounts for differences in color between ethnic and racial groups?

Although the number of melanocytes varies within anatomic regions of the body, interestingly, among different races and ethnicities, the actual number of melanocytes in the skin does not vary with skin color. Instead, among variations, it is the amount and distribution of melanin produced that changes. In mammals, two types of melanin are produced by melanocytes, eumelanin and pheomelanin. Eumelanin is a tyrosine-derived, dark brown or black pigment. Pheomelanin, derived from a biochemical shunt in the normal melanin production pathway, has a yellow to red-brown hue. Pheomelanin is the predominant pigment produced by those with freckles and red hair. It is also increased in Asian skin, and in women when compared to men. Melanin is packaged in melanosomes, which are membrane-bound vesicles containing a unique scaffolding of matrix proteins. Melanosomes within keratinocytes of white skin are distributed as membrane-bound clusters. In black skin, melanosomes tend to be larger and more diffusely located in the cell. Therefore, the quantity and composition of melanin, as well as melanosome size and distribution, vary considerably within the epidermis, both with ethnicity and with chronic sun exposure, yielding various degrees and hues of pigmentation.

Thong HY, Jee SH, Sun CC, Boissy RE: The patterns of melanosome distribution in keratinocytes of human skin as one determining factor of skin colour, Br J Dermatol 149:498–505, 2003.