Some of them get answers but I think there’s a question that might be never answered:
Why does so many character’s hair change the colour?
- Arima: Dark blue – white
- Yamori: Black – blond
- Uta: Blond – black
- Other CCG dude who got friends with Arima in Tokyo Ghoul:Jack whose name i’ve forgotten: Bright orange – deep black
( excluding Kaneki ‘cause we know why)
Well, I think I can answer some of those questions!
Starting with Fura, Arima’s friend, I think that he might’ve dyed his hair during his delinquent days and now that he’s an adult that works a serious job he reverted to his natural hair colour,
I think that Uta probaly bleached his hair when he was younger – that seems like an Uta thing to do, judging by his fashion sense.
Yamori had black hair in TG Jack, and had white hair when we see him after his torture


So his hair probably went white during it – after all, it was serious enough to create the sadistic “Jason” persona.
Arima is trickier – it seems that his hair gradually whitened during the years between him being 16 and 30 or so.
After all, he went from

fully coloured hair

to slightly lightening hair,

to almost entirely white hair,

to fully white hair.
So, I think that he might have a disorder or is doing something to make his hair gradually whiten.