Racism is a hugely grey area and there are varying degrees of it. Attraction to certain races is definitely racism but its obviously not 'let's go beat that guy up cus he's different to us' racist.
There are a huge number of factors that would play into this. Opinions from friends and family and the media seep in at a young age and slowly they form a racial prejudices, you can be naive and call it a racial preference but it really is the same thing. How many movies portray male romantic partners as black or asian? Little to none. So the public in Western countries get very little exposure to the idea of having a male romantic partner who is black or asian. This is definately the main reason why white males are at the moment the most desired partners for women. Did you know for example, Jet Li was scripted to kiss a white girl at the end of the movie Romeo Must Die but the producers changed it to a hug instead because of how the american public would not be accepting of an asian male romantic partner. So it's a much bigger almost institutional racism that's widespread and perpetuating but hidden beneath the surface. Media portrays blacks as unsuitable and asian males as desexualised, this forms public opinion, media then plays to public opinion because thats the only way they'll make money reinforcing the stereotypes and this is strengthened by the views of the people around you etc.
However, just because you are attracted to a race it doesn't mean necessarily that you are not racist against that race. Attractions to specific races, especially in cases of asian and black women, can be fetishes. The media teaches us that asian and black women are exotic and sexualises the idea of that and only that. It turns them into sexual objects to be dominated rather than human beings. At the end of the day, we should strive to knock down these romantic prejudices but there are more important racial issues at hand.