I'm not sure I agree with this. They may just represent conscious and subconscious racism, respectively.
In my opinion, I think the comparison to blue eyes or blonde hair or any other such quality is apt. But we need to follow this comparison through: if you said you preferred brunettes to blondes generally, no one would have a problem with that. If you said you were never attracted to blondes, though, that would strike most as a peculiar mental block.
Similarly, if you generally prefer the look of black women to asian women, or white women to Indian women, ceteris paribus, then there's nothing wrong with that. But if, for all practical purposes, you never find white women or black women or asian women attractive, then there is likely some subconscious mental block.