This happens a lot though. For example, the alleles that keep domestic cats and dogs friendly are from juvenilizing mutations. These mutations also make the ears floppy. It's called "neoteny". The same thing happened when the Russians domesticated silver foxes[1][2].
Humans are subject to a lot of these effects. Our head shape is very similar to the head shape of a baby chimp or gorilla, which obviously changes later in the ape's life. We have much smaller teeth and jaws than other apes our size.
Anyways, the point is that many alleles can be linked to a specific gene, so the fact that blue eyes and blond hair become more prevalent when less skin tone is selected for makes sense.
That said, I don't agree with some of the points made. He's kind of jumping to conclusions. You really can't rely on art to guide your research on skin tone. I draw art where humans are #FFFFFF because that's the color of the paper. Nobody in their right mind would trust something as symbolic as art.
I think the theory as a whole makes sense, though. Grains can grow, need moar vitamin D, lighter skin, other alleles come along for the ride. Now that's a pretty valid theory IMO.
I felt this is a bit of a loose statement. I would think, like light skin, there would be a reason a recessive genes became so prevalent.
Edit: spelling