Awesome, thanks for the pics!
That looks pretty cool. I'm definitely going to try this out sometime within the next week(I'll experiment with various colors), and I'll post pics when it's done.
EDIT: I couldn't wait any longer, so I went to wal-mart and picked up a multi-pack of Sharpie markers(fine point), and some scotch transparent tape.
I must say it was a HUGE pain trying to get the tape in there and get it to stick, without covering the 4 contact points for the trackball rollers. I used 1 layer of blue sharpie, didn't coat the whole piece of tape...just the area over and immediately around the LED. I took a picture of my phone, in the dark. See below.
I got to thinking. If I could find one of those cheap flashlights with the flimsy/thin interchangeable colored lenses...I could cut one to fit in that trackball area perfectly, with the corners cut to fit around the trackball roller contacts. Already colored, flimsy yet fits in there flush and won't fold or move...and light enough for a trackball push to be transferred through the lens to the actual button. Plus it's lens to start with, so it's meant for light to pass through it. Would be nifty, I'll see what I can come up with. ;)
Pic-