Red lights at older steam engines - how to model?

[Puddlejumper]

As for the lenses on the PRR locos at the RR Museum of Pa, you'll notice that they aren't the same on all the locos. It is pretty well believed that the RRMofPa (or the Penn Central prior to donation) used what was available to fill the openings of the lamps since they didn't have all the right colors. In practice the PRR used the same colors as everyone else (green, white) and used red for when an engine was running light or pushing on the rear of a train. I do believe they used blue in Kersone days to get green, but after the electric lamps were invented the lenses would have been green.

Dave