The retailer says they work only with white LED's, but I've seen them with other color LED's.
Colors do get distorted with other color LEDs
I don't own any thick PBT to test out if they fit, but if you look at my pictures, they fit on the side of the switch with a little bit extra sticking out.
I haven't talked to the people who make them, but if we can't get a deal, the price for 10 covers won't go over $1 $1.50. (.75 for cover, .4 for shipping to here from china, and the cost for time and packaging etc.