Why do people think that only mixed black girls are pretty?

well the thing is when ever a dark skin black girl is found pretty its always said to be "she has white features" how does that work? shes black.. she has black features just not the stereotypical ones. personally (im asian) im jealous of some black peoples skin tones. especially the ones that are medium to darker brown. light skin is also pretty along with super dark skin. at the end of the day there are very dark mixed girls and very light full black girls. some have small noses some have big noses. some have long hair some dont. what im saying is black people have the most exotic features so you really cant group them up into one group cause their looks varies. its no doubt black girls get the harshest reps cause media, personally i live in california and im friends with plenty of black girls and guys (light and dark) a lot have great grades, sweetest people ever, pretty, well dressed. so im just saying ive came across more white people with bad attitudes does that mean i should think all white people are bad and if they look stereotypical white with blonde hair and blue eyes they are worse than ones with brown hair and brown eyes.. NO! cause that would be retarded. yet thats what people do to black people (and even some latin) everyday. there was actually a study in i think 2010 where they altered black peoples skin tones. they made them white, or tan and asked a group of like 40 guys which girl is prettier (they put the altered picture next to pictures of real white, asian, latin pictures) and 8 out of 10 times the black girl with the altered skin was seen to be the prettiest. then they switched the skin tone back and asked and the black girl was only chosen 2 for ever 10 times. so it really shows its all in their head.