When I did my lighting I had a few choices I wasn't sure how head turn out, but now after some time, I think I found what I'm going to go with. Since there's no insert for the Gem shot, I wanted to make it more apparent.
I have the Gem figure attached by the shot, but wanted more. So, I have three different colors I tried to color the GEM insert and the lone GI bulb that's exposed to the eye in the loop. I first tried Cyan, which I graciously got from Comet as an add-in (Thanks!). This was too close to the green bulb I have in the opposing side GI slot for Quorra. So I tried both the turquoise and teal from pinball center. At the end, the turquoise won since it had the biggest difference. The frosted bulb is easy on the eye and the color match to the insert makes it that much easier to point out the Gem shot to anyone.
The next was that I went for various colors under the disc when I installed the clear rubber. I tried UV, purple, red, and pink. I ended up on Pink in the back and red in the front. A good mix of bright and red. I then opted to go yellow on the left sling area instead of orange. This made it brighter, but this is also where the optix Maximus killed it. Normally yellow and orange always disappointed me for output, but these blew me away. Didn't feel weak and were a great shade of the color. Doesn't make me feel like I color bombed it since it isn't dark, and it holds different than he other orange areas (zen and Tron targets).
I did the same with the inserts too, I made the clu heads orange and light cycle yellow and it really worked out well to give me different colors for each insert. Couldn't be happier with my Comet LED experience.