Anyone know the reason for the Blue lens in early brass rear kerosene tail lights? The rear is red and the side is clear to illuminate the license plate. In nautical use, the position lights are red and green, but blue is not in play here. Perhaps the glass could have originally been green and over time has become blue. I have asked several knowledgeable T persons and each has not come up with any answer. Just curious. Thanks in advance for your thoughts here.

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You have forgotten Grade 1.
Blue and yellow makes green. Blue glass , yellow flame

After reading both topics I am going to throw a monkey wrench into things. My grandfather had a blue stop light (stop cast into the glass).

All railroad lamps were blue also, the flames were yellow and the lenses were blue= green. Then the electrified lamps were the same, yellow light bulb source, plus blue lens=green....go to go!

But yellow flame + red lens should make orange light, right?

Not exactly Bill, a red lens will naturally filter out and only pass all but the red light in the spectrum

Cool! Thanks, Peter!

Bill..here's a shot of Pete's tail light lit up after arriving home from a dusk drive. Unfortunately I don't have the view from "the blue side". Hard to believe how bright the little yellow flame actually makes the red (and the others too) show up!