Maybe during glacial periods, ancient Asians and Europians moved back to Africa. When you mix all the different colors of people together, what do you get? Black!
Skin color is a local adaptation to sunlight (darker skin preferred) and vitamin D production in the skin (lighter color preferred). Mediterranean groups with tanning ability split the difference, and can adjust to the annual cycle.
Well, to start with for a long time the only “color” found in human pigment was black. Last year they reported that some have red pigment.