It is preference. To think otherwise is idiotic and missing the point of how preferences work, especially sexually-based preferences. Some women don't like men who have ginger hair. Some do. Some men don't like other men with larger genitals. Some women like tiny genitals. Is it not, then, by extension preference for/against skin colour? Is it racist to prefer women of say, Korean descent over other women of Caucasian descent?

Hint: it isn't. The human mind is mostly unmapped, uncharted territory with a crude crayon-drawn map called psychology to guide us. Preference is something that is shaped and molded during our formative years up until the day that we die. It's why some people derive satisfaction from feet or having their nipples whipped with a day-old sausage. By extension and the barest fundamentals of logic, we can extrapolate that preference for skin colour is not, in fact racist, but is instead the same as any other like or dislike.

Mine is from a tabletop character that I play. Kz'than, of a universe-specific insect race.