In other news, I just went through the entire Power Dyes Your Hair trope on tvtropes and this might legitimately be the only anime/manga example of a power-up darkening a person's hair
a LOT of hairs turning white, less but numerable hairs turning blond, several hairs turning pink, then some hair turning to a brighter shade of whatever it already was. One or two where it was something weird like red turning blue or blond turning bright green that didn't specify if it was a darker shade or not.
in bleach isn't there a fight against a guy who's power is "becomes god" and the solution is to pull out the unrevealed shikai that has the power to kill god?
past that i can think of a few instances where hair color changes were indirectly related to the power instead of directly (hair going white from necromancy/eldritch knowledge/etc), or where it's indicative of plural alters taking front and not technically powerup
was its power just "fuck this one guy in particular"?
just a lil desaturated
i suppose eevee evolving into umbreon doesn't count