The premise makes me laugh. It's a good story, but the mistaken identity of two people shown in the manga to have very different hair colors would not happen even with terrible vision. I'm legally blind without my glasses and you can bet the amorphous blob of a person I see would still have a brown blob of hair or black blob of hair. People look like a hair color blob, stacked on a skin color blob for the face, stacked on a blob for pants. They'd just look like blobs of brown and black and not hair in this case, but you can still see color even if your eyesight is awful.
Kijima-kun