I don't think all these explanation are true..
Well, nowadays....
C'mon, like people would really lose they time by thinking at this all.
I'm asian, and I want white skin so that it could contrast with my hair color.( so that I could look like Snow White
)
As for my caucasian friend, they want tanner skin because they think they are too white( like a ghost).
But reason is different from anybody.
Some white ppl would want to stay white. and some dark skin ppl wouldn't care if they were darker.
that's it.