system
A chat on subreddit /r/NoStupidQuestions
human
Red has been the color of danger- blood- since time immemorial, so it was natural to adopt if for "stop" on railroad signals and then traffic lights.

Green is much more recent and the association with "Go" or "Good" comes to culture from traffic lights, rather than being adopted for traffic lights from culture.

In the original railroad signals Red meant "Stop", Green meant "Caution" and White meant "Go". The problem was that even in the early days there were a lot of white lights around, and then a horrible railway accident happened because a lens fell off a red stop light and the engineer thought he had a go signal.

If we were doing it now we'd probably pick blue as the "Go" signal because of people with red / green colorblindness, but evidently they just didn't hire colorblind engineers. Back in the day cooler colors were less efficient to produce with lenses over yellowish light sources than warmer colors. A kerosene lamp or carbon filament incandescent lamp produces a lot of red and yellow, some green, and not very much blue or purple.
gpt
Green is also a perceptual peak.

For example early technicolor film was red and green only with no blue.  That's how unimportant blue is in our perception of color.  We can remove it entirely and have a reasonable facsimile of color.

So maybe blue might not be the best choice.  A blue-green like some traffic lights used could work.