I speak for a lot of users when I say.
No one is mexican
no one is cuban
no one is puerto rican
no one is asian
no one is african
no one is american
WHY?
there's no mexico
there's no cuba
there's no puerto rico
there's no asia (well...except for the land of the dragons...)
there's no africa (umm, where was Deep Jungle based from?)
there's no america
there is no race created for the KH world there for no one has a race. Just skin color and ethnicities to their respective...worlds.
as for the darker skinned characters
you've all mentioned a few and I'll include Rai, he has a nice tan going on ^_^
but you all notice that Kairi is the lighter skinned one of the three, Riku and sora, I would assume are darker because of being on the islands. Look at the official artwork and not hte CG, you can tell from the artwork better.
but hey, I guess it's just how you interpret things...