By Mike Fleming
Del Toro plays the title character, a Plains Indian member of the Blackfeet nation who returns from the WWII battlefield and experiences various medical symptoms, none of which can be explained physically. He travels to the famed Winter Hospital in Topeka, Kansas, where he encounters Georges Devereux (Amalric), a French ethno-psychiatrist considered to have a strong understanding of the modern Native American. Through their sessions, the two men, foreign to themselves and to their country, become friends.
His Wikipedia entry says:
On Facebook, someone said something about people who don't look Native still "walking the red road." To which I said:
I'm guessing Puerto Ricans like Del Toro don't look much like Blackfeet Indians, which is the tribe of his character Jimmy Picard. And since it's a WW II-era drama, Picard is that much more likely to be full- or half-blooded, not "white skinned."
More to the point, del Toro doesn't walk any red road that I know of. His looks are irrelevant because he doesn't fit the other criteria for being Native.
Most Latinos have some Native blood and are a tolerable second choice if a producer tries but can't find an acceptable Native actor. Most producers don't make the effort and simply cast whoever's convenient.
For more on casting issues, see How Hollywood Executives Think and Think Like a Man Shatters Hollywood Myths.