This is another member suggestion that also gets rave reviews on Amazon. Sounds like a gripping story and important aspect of our history.
Cane River, by Lalita Tademy
Lalita Tademy's riveting family saga chronicles four generations of women born into slavery along the Cane River in Louisiana. It is also a tale about the blurring of racial boundaries: great-grandmother Elisabeth notices an unmistakable "bleaching of the line" as first her daughter Suzette, then her granddaughter Philomene, and finally her great-granddaughter Emily choose (or are forcibly persuaded) to bear the illegitimate offspring of the area's white French planters. In many cases these children are loved by their fathers, and their paternity is widely acknowledged. However, neither state law nor local custom allows them to inherit wealth or property, a fact that gives Cane River much of its narrative drive.