I was just playing around with this kinda thing. I put two 15" green neons (not StreetGlows) under the dash, and two 15" in the back, under the jumpseat areas...super-bright, and pretty UFO-looking color! I then took out the three lights on the dome, went and got some green engine enamel. Made sure to tape up the metal/connection parts really good and then gave them a few good quick sprays. Next day, put the newly-colored-green lights back in the dome. The color matches the neons perfectly.
Now, what I did was get it wired so that the 4 'floor' neons came on with the dome light, as soon as you open the door. They then go out once you're inside. It's very easy to wire it so that when you turn on the switch for the dome, the neons come on as well. This is on a 2001 XLT. I dunno if I'm explaining that right- on the left side, there's the switch that turns your gauges brighter or dimmer and if you push it all the way on, then the dome lights all come on- that's stock. Now, you can wire it so that the neons will come on at the same time as that dome (which is cool-looking when they're all the same color)....