Well, blue or white hair suits Satoshi, ne?
I like him. I think if your hair/friend's hair turns grey, it would be a perfect prime for an actual hair dye from a beauty store, like Sally's beauty supply store where they have affordable quality beauty supplies like hair dye. When I had red highlights in my coarse hair, I had to bleach it blonde (nearly white) and add red hair dye (not Kool-aid). That lasted about 3 months with good Shampoo. Then it kind of faded to a copper brown.
I'm no professional. Just speaking from some experience.