Keanu is mixed-race, but he still seems to be an odd choice for Siddhartha, especially coming after Bill and Ted.
<edit>I should mention that he doesn't do a horrible job here, and I actually liked Little Buddha despite some problems.</edit>
Siddhartha may have looked more like Keanu than another Indian person. The upper castes of classical Indian society, to which the Buddha belonged, were mostly made up of the descendants of European invaders. Even today, there are a small amount of Indian people who look more European than they do South Asian.
Still, casting a white American as opposed to a lighter Indian person for the role is very weird. And I don't know anything about social mobility in classical Indian society, but it probably could be possible for a North Indian prince to have been dark-skinned.
Hollywood white-washing is an enormous problem, but I don't think this is the best example.