I can understand that they style character’s hair by their personality type and it makes more sense when trying to identify a character in high-speed action. Does anyone know the behind the scenes of why authors or anime professionals do this?
1. Young audience.
Now I will say that anime is not just for kids, Death Note is a prime example
but because of its young audience, they probably want to appeal to them with the crazy colours
they want to separate it from other animation or comics.
3. Fictional Fun
they can do so because the world is fictional.
4. they use the hair colour to represent the character's personality a lot faster.
5. to break racial stereotypes. – Amelia Arrows3 weeks ago
It really depends on the show. A lot of the time the goal seems to be telling the audience something about the character (for example, Todoroki's red-and-white hair in "My Hero Academia"). It may also have something to do with the fact that there isn't a lot of variation in hair colors in Japan to begin with--such that, for example, a Japanese person, until relatively recently, would be about as likely to see someone with blue hair as to see someone with blond hair. So, giving a character strange-colored hair (as opposed to the typical brown or black hair) is a way of marking them as exotic and therefore, more interesting. The vampire horror anime "Shiki" gives its characters strange-looking hair to make them look even more eerie than they otherwise would. – Debs3 weeks ago
In addition of Amelia Arrows' comment, I'd suggest that colouring the hair of female anime characters in school based stories also serves as a subtle criticism of the 'no dye' policy still strictly enforced in some Japanese schools. – Amyus3 weeks ago