Sounds like you have a version of DDE's like mine, the bulb lights up the fiber optics which run to the light housing, and into the rings.
Umnitza used to offer a package of colored film sheets designed for those light boxes - you can slide em in and change them to a ton of different colors. (red, blue, green, yellow, and alot of flavors inbetween). I just poked around their site and didn't see them, they used to come with the light kits I thought.