I'm confused, can someone tell me when did Maya's hair turned to black?

If I remember correctly, It's when Nemu started going to cram school. He died it.

It's in the main story.

no he stopped dying his hair, he has natural black hair

You are all right- ish
@ Corona- Bingo! He did dye it.
@Mimi- Correct
@Anon- He did stop dying his hair, but as Corona said before he had to dye it from blond to black.