I suspect it's the Massachusetts sun!
If it was a tan job, at least it was better than Kerry's, though I wouldn't advise following this strategy if Romney ever appears on BET.
They described it as a clueless Al Jolsonish attempt to hispander.
They've posted pics from earlier in the day to compare and contrast, close-ups, different angles...they're obsessing.
It looks like he stayed a little too long in a tanning bed (there is a distinct untanned area that a hat wouldn't explain.) It's the timing that seems to be an unfortunate coincidence.
This was when Kerry’s handlers were trying to pass him off as Mr. Athletic (a.k.a. The Most Interesting Man In The World). Toward the end of the campaign he was looking like his gas barbeque blew up in his face.