I'm what some would call "light-skinned", but my roomate is dark. People are always telling her that she is cute to be dark skinned, and while she thinks nothing of it, I find it offensive. She is a very pretty girl and her skin color should not defined her beauty.
In another case, a guy I met at the movies told me that he would not have approached me if I were a shade darker. I don't know what kind of line he thought that was, but I politely left him standing there looking like the fool he is.
But on a lighter note, I have a "thing" for dark skinned guys