IMHO, preferences are natural. The problem is in what we tell others (and ourselves), especially when we try to find descriptors that will exclude or discourage people from trying to get to know us.
1. If you're attracted to A PERSON, you're attracted to THAT PERSON. Don't try to break it down into their race, height, hair color, build etc because you will find exception after exception both in what you're attracted to and in your turnoffs. And then you'll wind up performing the typical mental gymnastics to try to explain what made that person different than the others. Not all people of a specific "race" have the same physical features or skin tone or personality or behavior and races are more mixed now than ever.
2. Is it ever useful to tell someone why you're physically not into them? I've never found it to be whether it was because of their body type, hair, race, height etc. In fact, whether physical or personality driven, unless someone asks AND unless it was something they could easily change, I have not once found it useful to tell someone why I'm not into them.
3. I've found that some of us get really disappointed when someone we're not attracted to hits on us and as a result we sort of try to punish them. This is a really crappy way to treat people who are into you.