Dear Matthew Alice:
How did the traditions of using red lights for stop and green lights for go start? It seems pretty arbitrary to me. But I'm sure there's some weird logic behind it. And that seems to be your department, so what's the answer?
-- Mark, Leucadia
You prefer maybe a nice Navajo white and, oh, maybe a deep mauve? Spare us designer traffic lights please. If you want the very old weird logic behind it, it goes back to all Western associations of the color red with war, specifically, and danger in general (spurting blood being a universally recognized sign that something's not going as planned). Newer weird logic is railroad logic. Red lights became the standard stop signals for trains in the mid 19th Century; red's complementary color, green, became the go. When Cleveland, Ohio, installed the first automobile traffic signals inn 1914, the inventor just borrowed an already established system.