You may want to look into the "frosted" part of the equation. I would check out a photography store, or a theatrical supply store that sells color media, and try to buy a sheet of diffusion media to put on the rear glass of the tank. There are many different types, so if you describe what you are trying to do (maybe take a picture with you) they should be able to hook you up with the right one... shouldn't cost more than about 8 or 9 bucks for a 20"x24" sheet. If they cant help, I can look through my swatch books to see if I can get you more info. I am interested in seeing if you can get this to work.
20Gal - 6 Harlequin Rasboras, 2 Triple Red Cockatoo Apistos , 1 BN Pleco
10Gal - 1 Orange Flash Cockatoo Apisto, 2 Amano Shrimp
20Gal - 13 Juvie Cockatoo Apistos... mostly Triple Reds
55Gal - Dry-Docked... wetness coming soon... I hope...