When Johns Hopkins University historian Martha S. Jones turned her formidable archive sleuthing skills on the ancestral history of her own family, she came across, at long last, a photograph of Nancy Bell Graves.

Graves, who was born into slavery in 1808, was the great-grandmother to Jones’ own grandmother. What the Civil War era photograph revealed was remarkable.

From the most distant branches of her family tree, Jones could see how often her family moved across the color line: the relatives who were enslaved and gave birth to mixed race children, the lovers who married in defiance of miscegenation laws and the family members who passed for white in some communities and Black in others.

Martha Jones writes in her new memoir  “The Trouble of Color,” “Nancy bequeathed to us not only her portrait but also the trouble of color —somewhere between too little and too much of it.”