I don't see it as racist. I was born back in the 50s, when nobody dated anyone outside their own nationality (Italian, Irish, Jewish, etc). Then it opened up in the 60s, and now, society is gradually coalescing as people find they're attracted to people of other cultures.
I rarely find it to be JUST about looks. Usually, there is some (cultural) trait that one identifies as attractive, along with the "looks."
The bigger issue is that, what some people identify as a trait specific to a "peoples" (as I call them, since race has been identified as a social construct), is sometimes a stereotype, such as Black men with big dicks. And that's all the person wants is their fantasy, and dismisses the nobility of whatever culture they "like." That, at least, approaches racism. It's like saying, "I only want this part of you: I don't value your cultural traits." People do it all the time, but when you're going into another group, sensitivity is required. It'll look like racism if you're doing that constantly. If someone likes Asians, and it's not stereotyping them ("I like that they're quiet and…").
I lived in San Francisco starting in the mid 70s until 2002, and the Asian Pacific Alliance guys, when we'd meet and compare notes (yup, we compare notes about White guys just as they do about minorities when they're alone) complained that the White guys stereotyped them all as "submissive" or "quiet" or something like that, and then, when they (the White guy) got the full personality of the individual guy, they suddenly lost interest in the guy because he didn't fit their stereotype of that group (fully racist, yes). As long as you have respect for the individual, fine. Frankly, Eminem is "blacker" than I am, and I think that's cool that he has so fully immersed himself in Black culture. I'd never think of him as racist because he comes across as Black-identified, yet dates (most) White girls. He's cool with me. A person can be racist in their friendships just as much as their romantic interests. As long as you are completely conscious about what you're doing, and why, I don't see anything to worry about. If you're on autopilot, though, be prepared for pushback from whoever you're marginalizing.
Otherwise, it's no different than only liking tall guys, or short guys, or blonds.