The photo in question

Other photos for comparison


I suspect that the photo was probably taken in a very well lit room, possibly during winter. I notice that he seems ruddier in that picture than the others, so the photographer may have played with the coloring a bit.
Personally, I don't think it is that big of a deal. Photographers play with skin tone all the time in photos. I'm sure they've gone darker and lighter on Obama's photos.