@chusetto actually they think it's for his own good. Because fitting in the group is very important in Japan.
Even teachers there, when they have mixed-blood students with foreign features like lighter hair, or even foreign students, actually advise parents to dye their hair black so they are not teased by their schoolmates because of jealousy.
It stems from good intentions, but fails to address the root of the problem, which is that Japanese society hates individuality.