There are a variety of reasons or excuses. Colorism is one and this occurs within many races around the globe. Other reasons include a perceived higher level of education, intelligence or wealth in lighter skinned people. Perhaps some people acclimate to a European standard of beauty while excluding their own? If so, they are likely turning away some great mates just because of color of their skin. Oh the horrific irony!
Also, some dark skinned people say they only want to be with those who are lighter skinned than themselves because they have experienced racism and do not want their children to endure as much racism as they did. I guess the intent is admirable but this plan of action is racist as well. Why limit yourself to certain colors of skin? Is your mate not MUCH MORE than this?
I think everyone should date who they are attracted to no matter what the color of that person's skin is. If anyone is saying they stay away from a certain skin color or skin colors, that's damn surely their right but it's also a great limitation in finding true love. But, if they are seeking a status symbol, I guess they know nothing of true love?