Re: Matt Smith's Departure Confirmed.
A black or brown Doctor walking around freely throughout history really isn't that unrealistic. He is generally well dressed, well spoken, has the proper paperwork to be whatever he needs to be and speaks with enough authority to make just about anyone think twice about just arresting him and tossing him shackles. There are a few particular points in history he might want to be extra careful in, but I'd imagine being white would have its downfalls in certain times and places too. Unless he pulls off the "I am the harbinger of your god" maneuver every time he runs into a pre-colonial non-european society I should think most of history is actually just as dangerous as a white man.
"There is no reason why good cannot triumph as often as evil. The triumph of anything is a matter of organization. If there are such things as angels, I hope that they are organized along the lines of the Maffia." - Winston Niles Rumfoord.