And just to be clear, I'm referring to roles where the ethnicity
is a fundamental motivation for a character's actions. Unless, of course, it's intentionally reversed to make an artistic statement-- like Patrick Stewart as Othello, with an otherwise all-black cast.
So if someone did an avante-garde production of Ragtime where all of the actors were black except for characters like Coalhouse, Sarah, and Booker T. Washington, that'd be one thing, but all-white? That's a little much.
Granted, there are shows, like Little Shop of Horrors, where you can conceivably have Crystal, Ronette, and Chiffon played by white girls even if that's not how the role was originally intended, and in Les Miserables, casting actors of multiple races was pretty successful-- the only time it felt weird to me was when a child character "grew up" to be someone of a totally different ethnicity.
When I was little, I used to watch the version of Cinderella with Brandy, and I never really thought of the fact that the characters who were supposed to be related were different races(though I was still frustrated that Cinderella wasn't blonde-- ha!), but I think if I was older when I saw it for the first time, it might have been distracting. (Victor Garber + Whoopi Goldberg = Paolo Montalban?)
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy