I was recently reading about the life of Aaron Burr and came across an interesting fact about his illegitimate children. His two illegitimate children, John Pierre Burr and Louisa Charlotte Burr, were born to a servant of Burr's from India (Wikipedia says perhaps Calcutta). It appears that both of his children later identified as black, including marrying African Americans and becoming involved in black culture, including the abolitionist movement. Of course, our modern cultural perceptions of race make a significant distinction between Indians or other non-African people with dark skin and blacks. Were Indians and other people with dark complexions (such as aboriginal people in Australia or Fijians) commonly viewed as blacks in the past? Are there other cases of Indians or other ethnic groups identifying as black in colonial or post-colonial America? Could someone in one of these groups choose how they identified or was that decided for them by their appearance/skin color? For that matter, how many Indians were there in the Americas at the time?
Our racial categories are socially constructed, and not as biologically-rooted as racists like to believe. Throughout American history, there are innumerable cases of individuals who slipped through as the cracks of the black/white racial dichotomy. Interracial sex and rape were so common in antebellum America that many black people did not look black by our modern perceptions, allowing them to assimilate into white society. One interesting example are the Melungeons and Lumbee people of the upper South, groups of mixed-race people who lived in distinct communities that could not be classified as either black or white. In other cases, people who did not easily fit into either side of the American racial dichotomy were just considered black.
Because they were dark skinned, or at least born to one dark-skinned parent, Aaron Burr's children would have had blackness attributed to them despite not fitting our modern definitions (which are ostensibly based on genetics rather than appearance). Because race is defined by perception, the attribution of blackness toward Burr's children would have led them to self-identify as black.
Interestingly, the descendants of South Asians workers in Louisiana helped form the Creole people - another heterogeneous ethnic group who identified as a distinct race, but were generally considered black by outsiders due to their dark appearance. This is quite similar to what happened to the Burr children.