Fairest of them All!
The official claim is that we had dark skin, but became fair-skinned only recently.
Why? Because we went from eating a lot of fatty fish to becoming farmers, and since we then no longer got all the vitamin D we needed to survive, only the fairest amongst us survived, and in the end we were all white. Hooray! Makes sense, right?
There are a few problematic facts in relation to this hypothesis though. First of all, not all Europeans became farmers at the same time, and some even never really became farmers at all… but they ALL became fair. And the ones who kept being hunter-gatherers the longest, and who never stopped eating plenty of fatty fish, like the Northern Europeans, became "fairest of them all".
Take Norway for example. It is made up of mainly mountains and fjords, and only 3% of the land is even suitable for farming. Norwegian farmers are even to this day also hunters, fishermen and gatherers. The Norwegians never stopped eating fatty fish… but they have always, from pre-historical times to present day, been fair. In fact, in terms of fairness, only the Swedes and Finns are fairer, and only by a tiny margin.
So if this hypothesis had been true, the Northern Europeans, and in particular the Norwegians, would STILL have been at least fairly dark, but the OPPOSITE is the case. We are "the Fairest of them All".