No, Native Americans are not black.
gotta be specific. Some of them might very well have been black , especially on the caribean islands and eastern tip of southamerica.
Its really not that difficult to cross from Africa to South America or Africa to cacribbean on a boat. unintellegint animals and plants native only to africa have made the trip, so im certain human beings could do the same with actual boats from west africa. Its almost gaurunteed that some folks shipwrecked and drifted in that direction due to ocean currents. Whats quesationable is whether there were intentional efforts, like the chinese trip to California under Zheng He.
But realistically, it can only be that region of the western hemisphere closer to africa. I have no confidence whatsoever that the rest of the native americans on either american continenent are black. I mean you can look at the unmixed ones if you go to rural nevado, idaho, arizona, and newmexico and there is nothing black (or white) about these people.