I feel like he would look so much hotter with black hair

Honestly there's a good chance he might dye it back! Narratively, he probably went lighter in the first place bc he was 'imitating' his brother. Or more accurately, he was shielding himself by wielding a persona similar to his brother. When things get better and he can be a more honest version of himself, I think it'd make sense for him to go back to black(aka true self or the more honest version)