Painting ambient lighting can be a bitch to get to look right. You have to pick the source of the light (in this case the plasma gun) and then figure out which surfaces would be hit by the light.

I suggest checking out the 3 spray primer theory too. http://www.belloflostsouls.net/2010/...-skylight.html

This list pretty old, but it's awesome and I've always wanted to try it. It should make painting a crap load of Ambient lights a lot easier.