>>82275265
These characters with bizarre haircolors most of the time canonically don't have it, as in in the live action film Misa just had black hair like everyone else. I doubt the point is also that the character is wearing yellow contacts.

It's just there, like Milhouses's blue hair, you're just not supposed to think about it and it's just there to make characters visually more distinct though sometimes they even talk about it in universe and describe someone as having blue hair who was literally born with it.

Yui was literally born with yellow hair and wine-colored eyes and all the other characters also have purple hair and all that kind of stuff and had it since childhood. You're just not supposed to think about it, that's all.