Three primary substances contribute to the coloration of skin tones; melanin, oxygenated hemoglobin and carotenes.
Melanin has the greatest effect on skin tone. The cells that produce melanin are the same in all races, but the amount and colors produced can vary greatly. Color can range all the way from black to tan. Two variants of melanin effect skin tone. One is called eumelanin. Emelanin is most abundant in people with dark skin. The other, pheomelanin, emparts a pink to red color and, therefore, is prevalent in red-headed people.
Hemoglobin has the next strongest effect on skin tone. When well-oxygenated, it is a bright red. We associate good health with the rosy complexion it produces in light-skinned people. Poorly oxygenated hemoglobin can cause the skin to take on a bluish tone. Because of it's weaker effect on skin tone, the influences of hemoglobin are generally only apparent in light toned people.
Carotenes provide the weakest contributor to skin color. They impart a yellowish tone that can be increased with the consumption of yellow foods such as carrots and oranges. People with darker skin tones generally do not exhibit the influence of carotenes because the stronger melatonin pigment will mask it.