I use a round glass plate for this work. Furthermore I stuck colored spotlight leaf on it. The colors are great. The leaf is heat-proof up to 200°C. I get it from ebay.de.
I put one in my Fibre Space (first edition) and one in my Jupiter 2. Both lamps only got 4 colors and now 10 like the color wheel from the fibre Space sec. edition. The flowoflava webpage inpired me. Thanks.
Clear, yellow, orange, red, pink, purple, dark blue, light blue, turquoise, green.