Responses
I can't remember if he dyed his hair...
https://www.mangago.zone/read-manga/mochizuki_san_ka_no_yankee/
No this is not it. Thank you though. I believe the title translates to “We started an affair” but I can’t seem to find it.
It is a SHOUJO manga. The FL plays this Otome Game and the ML is a delinquent, I think. He has dyed hair but dyed it back to black for the FL when he confessed.