Not necesarily, but it might be it, unconsciously. That's just my opinion and not for every case.
On the other hand, I don't think you have to feel guilty about it, it may be just genetical o biological. Not everybody is supposed to be the same and have the same patterns of behaviour/tastes.
In my case, I used to be like that, but later I evolved into loving all kinds of ethnics.
I find myself specially atracted to hibrids, but not exclusively.
I think it's pretty honorable that you stop and question yourself about it. I'm pretty sure it's completely possible for a person not to be racist and just feel atracted to women of its own ethnic group. You are missing a lot in my opinion, but hey, tastes are tastes.