Ugo.com has posted an interview with the A:TLA track team
. Amongst a lot of stuff about the awesome music that we know and love is this quote by Benjamin Wynn about starting up at the beginning of the series:"We went out to lunch and started talking about the show, how the story takes place in an alternate world and the characters. Everyone is ethnic...Asian, but not from any specific Asian country. It was kind of like a non-descriptive ethnicity."
So... yeah. I'm not exactly sure what he means by "non-descriptive ethnicity," but he still says that all the characters of Avatar: the Last Airbender are Asian. I suppose based on this quote you could cast them all from India or Thailand or Mongolia if you really wanted to, but the point remains; Aang is not white.