Maybe, but then I’d be concerned that people could easily abuse the system since just anyone could show up in a certain color hat or shirt.
I was thinking more along the lines of those height check wristbands they give kids - measure the kids once and give them a wristband, so then ride operators don’t have to measure them again and again all day. In this case, people would only have to demonstrate they can’t wear a mask once, get the wristband, and then avoid being confronted the rest of the day. It’s not a perfect system, but it might make the day less inconvenient for people who can’t wear masks.