The silicon caps are colour matched to each other. For example, when you get multiball, both MOVIE MADNESS and CREATURE FEATURE will light up at the same time. I am pretty sure RESCUE does as well (my memory is foggy). These all have green silicon caps. This is the most obvious one as it was designed into the lighting effects. The lighting on the pin will all go out at first except for these lamps. You'll just see the green lamps flashing to give the pin that creepy monster feeling as multiball is about to start.
BIG MILLIONS and UNLIMITED MILLIONS will also both light up at the same time when you have the ramp scoring feature going. Both of these have white silicon caps and flash during the mode along with the two ramp flashers underneath each ramp. SUPER JACKPOT is also white. It's at the top of the sign and matches up with the BIG MILLIONS and UNLIMITED MILLIONS.
EXTRA BALL, MULTIBALL RESTART, CREATURE FEATURE are all yellow. These are the modes that are lit most of the time. CREATURE FEATURE barely stops flashing the entire time you play the game.
JACKPOT is RED. This one makes the least sense as it's the one with the starkest contrast on the pin. However it's the one that most Creature owners seem to be in agreement on. The colour is red. My only logic for this one is because JACKPOT is in red font on the snackbar sign, the dome on the snackbar is red. It just makes the most sense as the colour choice.
Often you'll see a blue silicon cap on the SUPER JACKPOT. The blue silicon is even mentioned in the manual. However, to me it doesn't make sense to have blue as it's the least eye catching colour for such an important shot. This is the one sign lamp that is debated the most often. To me, it makes the most sense to be white as it matches the lamps on the other two signs, it is the brightest for such an important shot, it's shown on the official flyer as being white, and the photo evidence on the internet confirms it.
The only other sequence of silicon caps that makes sense to me is this one (below). Where the silicon caps are the same on all the signs, except red replaces the white caps but even this one shows the SUPER JACKPOT as white with blue no where to be seen.
Hey, but to each their own...
Here's an older thread on it, but it just adds confusion. The last pic is definitely wrong though. You would see a green and red lamp during multiball start and that would just ruin the esthetics completely.