Mcsweeneys:

Is Johnny Depp Native American or Native enough? Does he, like so too many others, have a distant Indian princess in his lineage? He’s said his great grandmother is Creek or Cherokee. Creek or Cherokee. He’s not sure which—this Creek-or-Cherokeeness of him amounts to one line on his Wikipedia page.

Why is it so many white Americans proudly claim to have a some amount of Native American blood in them? Many black Americans also have Native Americans in their mix, but they don't make as big a deal of it as whites do. I think the answer is found if one first considers how white Americans less eagerly and frequently declare or try to discover their black blood. This lack of enthusiams has, I think, less to do with racist feelings and more to do with the fact that black Americans are still around in great numbers. As Bob Marley put it, they are the survivors, and the reason for this has everything to do with luck rather than the will to live...
In 1517, Fray Bartolome de las Casas, feeling great pity for the Indians who grew worn and lean in the drudging infernos of the Antillean gold mines, proposed to Emperor Charles V that Negroes be brought to the isles of the Caribbean, so that they might grow worn and lean in the drudging infernos of the Antillean gold mines. To that odd variant on the species philanthropist we owe an infinitude of things: W. C. Handy's blues; the success achieved in Paris by the Uruguayan attorney-painter Pedro Figari; the fine runaway-slave prose of the likewise Uruguayan Vicente Rossi; the mythological stature of Abraham Lincoln....

Because black are here and everywhere they make the history of their suffering present/real/unavoidable everyday. As a consequence, it's much harder for whites like Johnny Depp to romanticize black Americans in the way they can Native Americans, whose numbers are low.

This is what some white Americans must feel about the blacks they encounter: You were not supposed to survive the horrors our kind imposed on you. You are supposed to be practically extinct. And we are supposed to remember you fondly in movies and song, recall with great affection your former nobility and glory, and give you all percentages of our blood.