as far as I read, he started with black and white, then went all black and now he's white again. He mentioned something about the old doctor telling him that the RC cells affected his productivity of melanin but seriously, only bullshit to fill the inexplicable gaps throughout the serie.

I think his hair color explains his current personality but he started with black hair as a nerd while in re his black hair means he's badass and don't give a fuck to anyone, similar to Meliodas in dark mode. I don't get it >:^(