This is a decent explainer: http://www.todayifoundout.com/index.php/2012/03/the-origin-of-the-green-yellow-and-red-color-scheme-for-traffic-lights/ http://www.

This is a decent explainer: http://www.todayifoundout.com/index.php/2012/03/the-origin-of-the-green-yellow-and-red-color-scheme-for-traffic-lights/ http://www.todayifoundout.com/index.php/2012/03/the-origin-o... Red is associated with danger so it was stop. Go was original white. This causes problems because if the lens falls off, stop looks like go. I guess blue is probably hard to make out in daytime against the sky, or if it's raining. Not a whole lot of colors left after that.