Ages and ages ago, I was reading about the Angelina Jolie as Marianne Pearl thing which made me think. I didn't get to really think those things through, because of the whole moving back to America thing. It's kind of interesting which ethnicities people deem acceptable to "substitute" other ethnicities for.
As far as I can tell, black and Asian characters are ethnicities you can't put white people in. Blackface and yellowface have been attempted in the past, but is generally barred from mainstream TV and movies, because it's in bad taste, and more importantly, someone might sue.
However there are a ton of other ethnicities that are apparently more fluid. For example, look at the career of Cliff Curtis, who, for those of you who are wondering, is Keisha Castle-Hughes's dad in Whale Rider.
Mr. Curtis, imdb.com reveals is Maori, however, his acting career reveals he played Pablo Escobar in Blow, Amir Abdullah in Three Kings, Shiekh Faddallah in The Insider, Claudio Perrini in Collateral Damage, and Mort Whitman in Spooked. So that means a Maori actor has played, a Latino character, an Iraqi character, an Italian character, and what I assume to be a white character.
My point is that there are certain roles that casting directors consider to be racially ambiguous enough to cast people not of those ethnicities, and that's ok. I mean, how many Arab characters are played by South Asian actors? Or Latino actors? And also vice versa? My guess is no casting director would put a Latino actor in the role meant specifically for an African American. With Asian characters, yellowface these days takes the form of cultural appropriation, rather than actual yellowface. Although Angry Asian Man tells me that Rob Schneider does yellowface in I Now Pronounce You Chuck and Larry. (This is complicated by the fact that Mr. Schneider is part Filipino. But you know, that's just an investigation for another time.) However clearly Latino roles, Native American roles, Pacific Islander roles, Arab roles, and I would guess South Asian roles, sometimes, are all up for grabs. I would even be curious if Filipinos would be included in this grab bag of brown. Apparently some brown people in the eyes of the viewing public all just look kind of the same.
On the other side of the equation, I find it kind of hilarious that in Disney cartoons, voices are assigned to ethnically specific actors. Well, sometimes. I mean I'm sure B.D. Wong and Ming Na Wen are happy for the residual pay they get from Mulan reruns, but still, what is so ethnically specific about an Asian American voice, and if there is one, why is Eddie Murphy in the movie?
And then of course, there are headtrippy, well ethnicity-wise anyway, movies like The Matrix, where a black man plays the Yoda/Mr. Miyagi role, and some part Asian guy, passing as white, takes on the Karate Kid role. Does Keanu Reeves count as Asian either? That's also a story for another time, I think.