I think you are mixing different things here.
Look again at white women. They diggin us way, way, way before it was ever acceptable for them to bring home a Black man. Is it even acceptable now? How were they programmed in this?
Mexicans are for the majority racist against themselves. You'll never meet another nationality that suffers from so much self-hate when it comes to their color. They dont count as an example when we discuss race.
Back to the issue. What is acceptable, as in who you supposed to bring home, is one thing. Who you are attracted to is another. Are you telling me that your friend went on to never be attracted by any woman darker then him? If that is the case I feel sorry for him, but I doubt it is the case. We cant help what turns us on, I think, for the most part, because it comes naturally.
I can name a bunch things that is attractive in women that I was not programmed into liking, the same for my dislikes. Maybe I can only speak for myself here, but I know that I a light-skin tone is an attractive one, without comparing to others and not because it is lighter then others, its just a naturally attractive one.