Yeah, sorry, that's what I meant.
Even if your vision's completely monochromatic you could, for example, use a red gel to discriminate yellow from green, because green will go dark when viewed through the red filter. This tends to work better for things like LEDs, which usually have a single wavelength.
Swatch books of gel samples can be obtained cheap or free from suppliers of stage stuff. Might be worth playing around with.
My issue with traffic lights isn't that I can't tell what colour they are, it's that from a distance the green looks like a random mercury/tungsten lamp. If it's dark, I won't always notice that there are green traffic lights until I'm fairly close (or the lights change). Those reflective borders help, and should allow you to tell the lights apart by position.
And then sometimes, you get deliberate decoys:
They've got the masks the wrong way round, so the green standing man means 'cross' and the red walking man means 'wait'.
I reported this to the council a couple of years ago. They haven't fixed it.