Is there an easy way to do this? I looked up under the bumper and can find nothing.. Do I have to go through the trunk or something?

hmmmmmmm, not sure what model you have but I have an '87GT and there are two license plate lights each held on by two phillips head screws and they are screwed into the license plate lamps from the outside of the car.......

I changed out mine recently and added some purple like color bulbs. But for some reason they still shine white. Can the outer clear part be painted to make sure they shine with color or what?

I think I read somewhere that the police don't look favorably on people messing with plates or the lights that illuminate them. I got stopped once cuz mine were out, but they were working... just a little trim paint overspray made them really dim.

The 86 I took apart had Torx head screws visible by looking up by your plate. Remove the screws and move them around and work them down through the opening. Then just twist the bulb socket 1/4 turn and they pull out, then replace the bulb. It really is fairly easy. Good Luck.
Harder to explain than DO

Are the later models rear bumpers that much different ? In my 85 GT I can easily reach up with a couple of fingers and twist the bulb sockets out. It's a bugger to get them back in though..