I thought I knew til I re-read your question. I don't have much experience with the GI.

Buy a cheap o power converter board. They are on amazon for like $5. You can set an input and output voltages

Comet pinball has led strips for that voltage.

check out terminator 2 pinball club lots of info and pics. joe

Realize this is an old thread, but I've been tinkering with the flashers a bit so interested to hear what others say.

I think on the first question, if you get an rgb strip, you can solder four wires to it (one hot, one for red, another for green and another for blue. run the positive lead to a hot lug on a flasher and run another lead to the ground lug on that flasher and then the two others to the ground lugs on the other flashers where you want the strip to light. When the flashers are active, that color will flash.

On the second, You can't run a 12v led strip off the GI as GI is 6v. There are 6v led strips out there, but I don't think they are very common. Comet, cointaker and Mezel sell 6v strips in short lengths.