Our two cover inserts fit the same carrier. The wrong one even lets the sample sit flat. Someone has proposed green paint on the correct insert, but the recipe screen only names the carrier. That's a lot of trust in one paint mark.
Can either insert also fit backwards? Paint might help a person find the intended part, but you have two different mistakes to deal with if the same piece can go in the wrong way.
A key deals with orientation only if its design actually distinguishes it. I would also ask which insert identity the recipe is checked against; the carrier name cannot answer that.
I've asked tooling for the physical distinction and controls for the insert-to-recipe check. Keeping those as separate questions. Nobody gets to answer both with a tin of paint.