Let's see here. Pokémon is manga styled, yes? Ever wondered why there aren't too many coloured people in mangas or anime? Well, mostly because there aren't that many coloured people in Japan. The games are usually made to come out in Japan. And usually, skin tones are pretty simplyfied in manga. You're playing japanese people, and so the characters have the skin tone that is used in manga for most japanese. Japanese peoples skin changes in tone a little aswell, but it's usually not too noticeable in most mangas. (I'm trying to say this as easy as possible, hope I get it right.)
About the little more heavy people, again, it's manga. Kids just aren't... fat, in manga. It may be annoying, but I'm just saying it as it is.
So yeah, I'd like the ideas of a little minorities in the games too, but there are reasons why they don't have it.
And once again: It's RPG, you're not necessarily supposed to be playing yourself; but these japanese main characters.
But IF you were able to customize a little, that would be awesome.