I'm white and yes, I prefer the more mulatto black girls in general. I've seen some dark black girls that I thought were beautiful, but generally the more black black girls have facial features I'm not crazy about. I don't dislike the dark skin, it is more the facial features I like more are more common in mulattos.
"Is that somewhat more attractive?" Compared to other black women or...? If that's what you meant, I'm actually more drawn towards girls on the darker side when it comes to black women, but I like it all. A pretty girl is a pretty girl.
I don't know how a black woman can look mulatto unless she is. Just because a black woman is lighter skin doesn't mean she qualifies has looking mixed. We come in all shades, so to other races you are still seen has a black woman, no matter how light you are. It is our genetics that link us has being African American not our skin tone.
Has to answer your question, the only way I can see someone not liking someone of darker pigment is if they are discriminatory towards it. Just because your skin is lighter doesn't make you automatically more attractive. I can see someone thinking that if they have something against darker skin tones and are set in an ignorant mentality.