anime history - When & where did the unnatural hair color aka You gotta have blue hair trope originate? - Anime & Manga Stack Exchange

I specifically want to know which manga or anime started the trend, so I can reason from there to the how question, in order to not make general assumptions. There was a time in manga/anime where

Does the colour of the hair of the character always mean the same or some anime and manga made their own rules? - Quora

Why is it that anime characters are often drawn with unnatural hair colors? (pink, red, blue, and similar bright colors)? - Quora

Did the trope of 'You Gotta Have Blue Hair' originate in anime and manga, or can it be seen in enough older works to determine a different origin? Is there any official

Why can anime characters be born with any hair color? - Quora

Why can anime characters be born with any hair color? - Quora

Why is anime obsessed with colored hair? - Quora

Gintama 2023 Rewatch - Discussion] - Week 1(Episodes 3-9) : r/anime

Did the trope of 'You Gotta Have Blue Hair' originate in anime and manga, or can it be seen in enough older works to determine a different origin? Is there any official

Why do the main characters in anime have unnatural hair colors while background characters have natural colors? - Quora