I think it's OI, the FMC gets adopted by the duke, he's black haired and the moma is red haired. They have a daughter with red hair too. Daughter isn't close with the duke, and is trying to be perfect as an heir. Daughter and FMC become close, FMC dyes her hair rainbow by accident because ML is a lil shit. He's also supposed to be the villain, and is an ousted prince.
I think it's OI, the FMC gets adopted by the duke, he's black haired and the moma is red haired. They have a daughter with red hair too. Daughter isn't close with the duke, and is trying to be perfect as an heir. Daughter and FMC become close, FMC dyes her hair rainbow by accident because ML is a lil shit. He's also supposed to be the villain, and is an ousted prince.