The photocells in a camera sensors only pickup light intensity. The sensor itself can't distinguish color, only intensity. The way a camera sees in color is by placing filters over each photocell, and then measuring the intensity of that specific wavelength at that specific photocell. I highly doubt the system would be looking specifically for the color red (although it could use a red filter as a secondary validation), It would most likely be looking for the higher intensity of light coming from one of the three circles/squares in the traffic light. In the USA, traffic lights are always Red, Yellow, Green; either top to bottom, or left to right. Now, to complicate things, There are traffic lights with more than three circles/squares, and I don't really think there is a specific standard on that. I've seen different configurations of traffic lights with more than three lights. But, I do believe that the first two are always Red - Yellow, and then after that is where I've seen it differ with green arrows, or even a fourth light which is another red light....