Why aren't white men attracted to women with dark skin?

I see white men with white women and asian women all the time but I rarely see them with mexican, south american, african american, african or indian women. Are they turned off by dark skin?

When I say dark skin, I mean anything from dark olive to dark chocolate skin.

Would a white guy date a girl of this skin color (if she wasn't Beyonce)?
http://img2.timeinc0o0net/people/i/2007/sp…

Honest opinions please, I won't report you for racism, promise.