I did made my custom, by my self proly 6 yrs ago on my MBC280 (the reason I made it is cuz I wanted to use my OEM chrome frame and the wallMart and so on stores did cary only clears plasic plate covers which did NOT fit in any frame ).
Anyway you can get clear plexiglass from HDepot and tint it with car window tint (by your choice of % tint) ...... it is great on dark (my is black pearl) car with chrome L. frame and tinted cover on the plate ....
PS: btw for all of that yrs it did NOT crack or yellowed or peel off, the only small down side is when washing I'm getting soap inside (so you have to hose it a bit longer) , but that is also fixable by instaling weather stripping around
hope that answered some of your Q.