I've been thinking about this for a long time, thanks for posting it hehe. I think the reasons why people find attractive certain races are culture and the media. The truth is that a person of one race/ethnicity usually looks for another person of the same race/etchnicity. For example, I live in San Diego, and here are lots of mexicans, and you would think heyy soo mexicans and americans mix a lot!....Not really,at least not her. I mean, they get along, but talking about romantic partners, mexicans usually stick to mexicans and americans with americans or other races.
Actually, I've observed that americans mate with other races easier than mexicans with other races , I don't know why, but I guess it is because of the roots of Mexico. Not because we are racists haha. Mexicans are not so used to see different races in Mexico.
In mexico there are only mexicans, there is not a diversity like here, so you date a mexican or you date a mexican! So...I guess that, when they come here, and see a bunch of other mexicans, they stick with the ones they match "easier". Of course it's not a rule, but I think some people prefer to stick to the same, a lot of times unconsciously. I think the area where you are living influences a lot too, there are some areas of all white, all latino, all asian,etc. so when a different person comes, he/she might look very different at what you they are used to see.
Me, personally, I find attractive well...latinos, americans and sometimes, african americans( I think it's because there have been more whites on TV throug history idk); but I still would have to consider their personal traits(not to shound shallow) because you can't say you like ALL latinos, or ALL americans, or ALL african americans, maybe there's an african american who is more attractive than an attractive american and so and so. And well, that was my particular case
racism is different than just looking for "your type" and that IS wrong.