I think that it would partly depend on the acting ability of the person, and I am in no way a racist, but if the character is purposely meant to be white, then that would obviously be a preference for the actor to be white.
But it depends on the context as well. For instance, in a superhero film the fact that the character is white is probably not relevant to the actual story, it is just the way the character is designed, therefore there is no problem with black actors portraying white superheroes.
But if you think about things like historical documentaries, it is different. You wouldn't have a black person playing Henry VIII would you? Or a white person playing as black slave in a historical documentary, it depends on whether the skin colour/race/ethnicity is of importance to the story, and history of the program.