Your on the right track, but I mean one that fades from one color to another. BUt I think I might have come up with something. If you have 2 pots in the trem cavity. One on each side. Then 2 pulleys (one in each bottom rear corner). And a string tied to each side of the tremolo and wrapped around the pulley to the pot. Then the string is wrapped around the shaft of the pot. But heres the catch, one string is wrapped one way, and the oneo n the other pot is wrapped hte other way. So when the trem is making the pitch lower, one pot is turned up, and the other is turned down. And The first lug would be the power supply, the second lug would be the led, and the 3rd lug would be ground. Then the LEDs would both be behind a semi-transparent inlay, thus giving a tie-dye in progress effect when the tremolo is in action. Of course you would attach a spring to the front side of the trem cavity connected to a string that wraps around the pot in the opposite direction as the first string so it will go back to where it was in the first place when the trem is let down. I might draw up a diagram later.
Damn! Now all I need is a guitar with a tremolo.