Why do black people only have lighter skin on their palms and feet and no where else?

For what it's worth as a sincere fyi, you've got the broad direction of when, where, and how skin colors in populations developed backwards.
Modern Homo Sapiens, as best as current science can tell, evolved on the continent of Africa. Due to the large amounts of sunlight that would be received there, we naturally would have started as a largely dark-skinned species.

As we spread out, particularly to places with less direct sunlight, and interbred with other hominids, high melanin content would steadily be evolved out in those nearer-to-the-poles populations, and they grew paler. This seems to be due to the fact that vitamin D production, important for general survival, was hampered by the less direct sunlight we received when combined with heavy melanin content in the skin.

Hell, blue eyes, the eye color with the least melanin-content, evolved as recently as 10-6,000 years ago.

/r/NoStupidQuestions Thread Parent