Conan,
Yes, you should not be surprised if you are told to dye hair, but it can be easily solved without dyeing. And you should remember that our government clearly states that it's important that children are educated to acknowledge themselves as who they are.
(Backup is shown below where it says ‚ ‚è‚Ì‚Ü‚Ü‚ÌŽ©•ª‚ðm’è“I‚É‘¨‚¦‚é
https://www.mext.go.jp/content/20210824-mxt_jidou02-000017487_004.pdf )
Just for your reference, let me tell you about us. Our ancestors have been Japanese as far as we know, and my child was born with extremely light brown hair. At some of his schools, we did have to sign a note reassuring that that is his natural hair color, as opposed to being dyed out of bad influences such as gangster cultures, but everyone was always understanding and no one ever questioned his hair in a bad way. Everyone either loved his hair or just took it as granted - for 18 years - until a few days before his final graduation ceremony.
A couple of days before his high school graduation day, he brought a note home suggesting we need to have his hair dyed black. We were pretty shocked. It was that rare. And this was the only time in my life as a parent where I had to make a phone call to his teacher to firmly oppose to the idea. I'm very thankful that the one phone call worked, and that we didn't have to have his hair dyed.
THEN, to my surprise, it turned out that it was one of the (Japanese) parents who insisted that if you're "Japanese" you needed to keep your hair black. To that parent, it included those whose hair color had become naturally lighter from doing school sports club activities under the sun.
I'd like to take this opportunity to inform the world that a great percentage of people of Japanese heritage are born with very light brown hair and sometimes even blonde hair. In fact, the majority of Japanese hair is not pitch black. They're dark brown.
So, although most people with light-color hair never go through this kind of problem, you shouldn't be surprised if a small percentage of people happen to influence the majority to the point they tell you to dye hair. But you must remember, that it can be easily solved without dyeing.
I hope it helps.