I think that the most visible advantage/disadvantage of having different skin colors, are the frequency and severity of sunburns. Black people are more resistant to sunburns than white people. And given that they would need to move hundreds or thousands of kilometers, to be exposed to lower latitudes and heavier solar radiation, and that it was a loooong trip in those prehistoric times, maybe they didn't get to see the advantages/disadvantages.
How common were sunburns before indoor lighting and industrialization though? If you spent at least an hour outdoors every day from early spring through late fall would you ever get sunburned?
People have used protective clothing for a long time now. Farmers used to use big hats. I can't prove anything from 5000 years ago, but there was a kind of cowboy hat in Finnish farmer culture about hundred years back.
In my experience, no, although it may take a bit more than an hour each day and you may need to spend it outside during the "high noon" part of the day. Basically, I've often, in the past, jumped into spending a lot of time outdoors shirtless in the summer time and would get sunburned once but then from that point on would not. It seems that the sustained sun keeps one's "tolerance" up so that sunburns don't reoccur at least until the skin gets less tan again (when less time is spent outdoors)
I'm from India, and have never used sunscreen, as is the case with the majority here. We don't get sunburned that easily i guess. It does happen if we go into the mountains i.e. snow peaks is not that common otherwise.
But then again... who knows?!