Tony Mendez is (not "was" -- he's a living person, and Argo was not only based on his life, but on his own writing about it, and he was a consultant on the project and actively participated in its promotion as well as its production) but also a white American (he and at least his parents, on both sides, were born in the US) of Mexican descent on his fathers side and mixed European descent, not via any Hispanic culture, on his mother's side.

To say that having him -- not a character based on him but rewritten to be a different ethnicity, but a character which is explicitly the same Tony Mendez -- played by a white who didn't have exactly the same ancestry is "whitewashing" is reducing "whitewashing" to meaninglessness.