Personally, I think it's a cultural thing more than a race thing... In less developed nations, those who have fairer skin are considered to be more "beautiful" because it signifies that the individual is wealthy enough that they do not engage in manual labor (i.e. farming), whereas in wealthier nations, individuals with tanned skin are considered to be more beautiful because they (in turn) have the money to get fake tans. That, at least, is the gist of what I feel is going on. I don't think people consciously make these decisions nor do I think this occurs to most people.
Though it is true that race does occasionally play a role in this, the context is different. In the instance wherein race plays a major factor, the issue is more of cultural identity than fashion or looks per se. Lighter skinned black people for instance, are sometimes ostracised by fellow, darker black people because they aren't "really black". Now, these are generalizations and by no means am I making the claim that every black person feels or acts this way, but it does in fact happen.
Going deeper into this debate would entail that I write pages and pages of text, but since this is a forum, I shall end it here.. I hope the message that I was trying to get across makes sense.. and that it actually does get across.. 