Technically, indigenous Americans would have to include many Hispanics/Latinos since they are strongly tied to "Indians". And there isn't as much racial diversity in Latin America as there is here. There is a lot of diversity, but the populations are largely dominated by Amerindians, indigenous people, or mestizos. It varies wildly from country to country based on the type of colonial rule that existed.
Most Americans that identify as black who can't trace themselves to Africa within the last couple of generations are almost always fractionally 'white' genetically. The same is true of Native Americans, but perhaps more so.
