Naraku
Why does Naraku have black hair, And mystery villain revealed.
Naraku has black hair because he is the reincarnation of Gray, you see after his death during the Alverez War, Gray made a promise to Juvia that he would protect her forever, in the future Juvia never aged, so when Naraku became 18 he married Juvia, thus he witnessed Spoilers an unknown person kill Natsu and Lucy, and then rape Juvia in front of his eyes before killing her. It is not yet told who this person is, but I'm pretty sure you could figure it out, also I know he isn't a human but celestial spirit, any guess, It's Loke. Anyway if you don't want spoilers then don't read this update, also the story is not canon, because Loke would never do that, but he became corrupt with power and transformed into his Leo form, also Natsu has an emperor for similar to the Leo form in this story. I hope this answered the question, but there will more detail to this theory in later chapters.