That's more a case of selection bias. Those who had portraits made of them when they died, like the Fayum Portraits, tended to be wealthier Egyptians who weren

That's more a case of selection bias. Those who had portraits made of them when they died, like the Fayum Portraits, tended to be wealthier Egyptians who weren't outside working in the sun as much as the poorer ones. Also, the Fayum area that "Fayum Portraits" gets its name from is not too far from Cairo, which is in the Northern part of Egypt, where peoples skin color tended to be lighter than those in the far south of Egypt, as you got closer to what was Nubia.