It's a phenomenon where anyone's hair can turn white due to immense stress on the body or fear and such, it often gets used in stories. It's physically impossible the way it's usually presented, though. Your hair that's already grown won't just spontaneously change color from root to tip. Can't exactly make a visual impact in a story if someone's hair realistically started changing the same way it does when you just grow it out after dying it, though. Kinda takes a while, that'd be a lot of time skipping just to show one silly result of whichever situation it was.I dont get how he changed his hair color tho :u