At the rod shop I used to work at we installed what I think you're talking about on a 30's ford pu. it was a clear plexitype lens that you could mold to the contour you want. it was about 1/8" with a row of LED's behind it. once we cut the slot and mounted it it was sanded to match the style line and removed for polishing. after the pu was painted and the lens reinstalled, the plexi took the color of the truck and blended right in until you hit the brakes. It works better on solids than metallics, but will give the illusion of a painted lens. does that sound like what you're looking for?