It's not about percentages. A movie could have an all-minority cast except for one white guy, the problem is that guy will probably get the lead and most poster space. The Guardians of the Galaxy poster is one white guy and the rest are non-humans.
Hollywood seems to be going backwards on this issue. Just last year, Johnny Depp played Tonto. I get that this is a marketability issue, these are corporations just interested in making a profit, but it becomes a catch-22- minority actors aren't given the shot to prove their marketability. If Independence Day were made today, I'm not sure Will Smith would be cast as a lead.