I used to own a Scout II years ago. They're notorious for the tail light lenses fading.
One day I got tired of the look so I went to the Hobby shop in Campbell that's got everything under the sun. Bought a small jar of this Ruby transluscent Testors. Reduced it a little with laquer thinner, poured it in a Preval sprayer. Then sprayed the inside lenses.
Worked like a charm.