A very crude method that I once saw on a car, had vaseline rubbed on the inside of the windscreen. I later found this had been done to cover up the interior that had been hacked to bits to reduce weight!
Not really a professional way to do it tho. I once found some glass paint in a hobby shop and used that to paint the lenses of the headlights on one of my cars. It looked quite well.
Jimbo


Jimbo