I wonder if Heonjae has poliosis? I thought his hair being white was a choice or just his ...

It looks more like going grey early to me, poliosis is a lot more specific in appearance and this isnt it

I considered that but I did have a friend whose hair would have turned completely white a few years ago on his teens if he hadn't done "treatment for it" (?) I don't know what it was, either way it might get mentioned if there are more flashbacks
Heonjaes eyebrows also got white, man's a grandpa