Well first of all, beauty is subjective - everyone has different preferences. Secondly, it depends why these people you speak of prefer white women to black women. If it's because they believe that the white race is superior to the black race, then BINGO! They are 'brainwashed racists', as you say. If it's just based on personal aesthetic preferences, then it's not racist, it's just that, preferences.
Think about it this way: there are some white guys who prefer Asian girls just based on aesthetic and looks alone. There are some white guys who prefer black girls for the same reason. Are these people then racist against their own race? Obviously not. Same goes for black guys who prefer white girls and so on.