Watermelon Man (1970)

Jeff Gerber, a racist insurance agent and fitness freak, lives in a typical suburban neighborhood. But Jeff's bigoted world of taunting and harassing black people on and off the job is turned upside down when his skin inexplicably turns dark overnight. As Jeff tries to come to terms with this unexplained phenomenon that has befallen him, he soon becomes the victim himself, when all of his friends and neighbors suddenly shun and harass him.