I think criticizing someone for their sexual and aesthetic preferences is a really bad idea, and pointless besides.
I don't like blondes. I'd never go out on a limb and say that I've never found a blonde attractive - I have - but I have my preference. To me, it's no different from saying "I don't date blacks". In the end it's all superficial. If their feelings extend past that into outright hatred, that's racism. But simply having a preference? Not racist in the least.
Granted, in my experience when people go out of their way to mention "I'm not racist, though!", it usually means they are. But that's another discussion entirely.