When anything is black or brown, that means it absorbs all or nearly all the colors. When light hits a black object, none of the light is reflected back. However, in the case of skin, the actual color we see isn’t what’s important. That’s because we can only see a bit of the light of the sun called “visible light” which is the portion of light with color.

There is another part of the light called ultraviolet or UV light which has a much bigger role in the development of skin color. The evolutionary benefits of dark skin versus light skin mostly comes down to vitamins UV light is necessary for making vitamin D which is important for preventing rickets, which causes skeletal deformities. Therefore, to make vitamin D, light skin is preferable because it will increase your UV exposure. Although, UV light destroys another vitamin called folate which is important for brain and spine development in fetuses.

Also UV light can case DNA damage in cells, eventually leading to skin cancer. To prevent folate depletion and decrease skin cancer rates, dark skin is preferable. The earliest humans all had dark skin because folate was so important for having babies survive. Skin cancer has likely played little role in the development of dark skin since cancer generally affects people after childbearing years. Diseases that affect people after they have children generally can’t impact future evolution. However, once humans moved to areas with less UV exposure like northern Europe, vitamin D deficiency became a serious problem and they evolved light skin. So the benefits of dark skin are lower risks for folate deficiency and skin cancer, and the downside is higher risk of vitamin D deficiency.