I'm pretty sure it's just colored plastic, but I've got a suggestion that might work for whatever you're doing. I saw a project that someone did over at Xbox Scene, where he took the IR dongle that normally plugs into a controller port an permanently mounted it inside his Xbox, so that it would not take up a controller port. Really cool.
Anyway, he drilled a small hole in the front of the xbox case to allow the IR light through, and he just covered it up with a piece of exposed film (I think he just taped it on from the inside). It looked pretty good.
I hope that's helpful.