Possible lore might not be canon but its an idea.

Back during the medieval time there was a myth about a monster with white eyes, people call them the “Untoten“ (undead in German) they say the Untoten looks exactly like a normal human being, only way you can tell they are a Untoten is their eyes. If it glows white they are a Untoten.
This myth was thought to be a scare for kids, but it is a real thing.
I dont know how to like make myths so like this could be dumb lmao