Skin colour data obtained by reflectance spectrophotometry on indigenous populations are compared with environmental variables--latitude, temperature, humidity and altitude. Association with latitude predominates at all wavelengths. Temperatures show a small but appreciable association at the shorter wavelengths, humidity at wavelengths above 595 nm. Over 80 per cent of the total interpopulation variance at each wave length is accounted for by these variables, more at the shorter wavelengths. It is suggested that skin colour should be regarded as a complex of entities of differing selective values rather than a single entity.