its because it's symbolic. the characters with white hair tend to be insane or have lost humanity. when kaneki regained his sanity his hair returned to black. jizou has gained his sanity, and arima is just inhuman in strength
and fetus rize too
I guess I'd rather like him to get on with kaneki's story instead of making more insane characters that are almost all the same ...
It could also be the Maria Antoinette Syndrome: a lot of stress/ an extreme situation causes the hair to turn grey/white
((Kinda think that's why old people have grey/white hair))
yes I get that. But I'm pretty sure it doesn't occur that often. Also they don't grow back in their original hair color because they forgot the cause....
seems like the mangaka has a thing for white hair... srsly, doesn't he know how hair color works?