Ai no Kusabi
This futuristic tale is set in a world where men are assigned various social classes based on their hair color. Iason Mink, a high-class Blondie, runs into Riki, a black-haired Mongrel, and makes him his "Pet." As Riki learns of the dangers Iason faces by keeping him, he finds himself developing feelings for his master.
This is a remake of the 1992 OVA of the same name.