The legacies of slavery and racism are central to Light in August. Joe Christmas spends his life haunted by his blackness, the status of which is never actually confirmed in the novel. The book suggests that in 1920s America, knowledge about someone's race was much more about perception, hearsay, and opinion than it was about objectivity.
Christmas acts out his racial self-hatred by inflicting violence on other black people.
Whiteness is in the eye of the beholder.
Christmas refuses to exist as either a black man or a white man.