This guy makes decals somehow for his playfields. Not sure of the technique but Im pretty sure that a colored ring could be produced and put down and covered by a conventional mylar cover.
https://pinside.com/pinball/forum/topic/a-protector-decal-for-my-beloved-spin-out-em-purists-hide-your-eyes
Added over 7 years ago: I believe he does this for his own use and not as a business or anything. Just posted this to show what can be done.