Morning Star by Pierce Brown

Born a lowly Red in the mines of Mars, Darrow lost his beloved wife to the treacherous Gold overlords. Vowing to fight for the future that his wife believed in, Darrow joins a secret revolutionary group and is remade into a Gold so that he can infiltrate the ruling class and bring them down from the inside. Now, after years of hiding amongst the Golds, Darrow is finally ready to declare open revolution and throw off the chains of oppression. Nothing in Darrow's world has been easily won, and this final fight will be the most harrowing of all.