The genetic argument doesn't fly because we're talking about Galifreyan DNA, of which almost nothing has been revealed during the entire history of the franchise. The only thing we know for sure is he has two hearts. If House woke up with two hearts that would be ridiculous. If he woke up black, trust me, Hollywood writers would find six different ways to reconcile it.

Also against the genetics argument is the thought that, except for the Baker boys, none of the Doctors have looked anything like each other. I'd have less difficulty believing he could be black than I do of him regenerating from Troughton to Pertwee.

I felt robbed when late in the last series Tennant regenerated as himself. If they can pull a stunt like that, they can change his skin color.

But I do see your point about the politics, and agree that choosing an actor to appease some conceived racial imperative is a Bad thing™.