Ebony and Ivory live together in perfect harmony, so they have Interracial Relationships. Literally every companion save Amy Pond has had one since Series 1 (UNLESS you count Ginger as a race and then you can safely add Amy and Rory). Normally, I wouldn't think of it as a thing, but they've kinda forced the issue. You'd think that there was literally nothing but black and white people in Britain, or something.