Pick a likely time period your black Lewis family was in N.C. and then go to the census just before or after that period. Look for counties with the most (white) Lewis families in it, then look to the slave schedule and check out the Lewis families with the most, on down to the least. This might give you a target county? Jim
My ancestors were Mulattoes who were lived in Virginia. Two of those ancestors, Ambrose and Charles Lewis were in the Revolutionary War. They were brothers, born in King George County to a white man (John Lewis), and a Mulatto woman named Josephine. After the Revolutionary War, some of the family settled in Fredricksburg and others in Richmond. From those points they scattered throughout the US, Canada, and even Africa. Your Lewis lines may be connected to my Virginia Lewis lines. I will be more than happy to share information.