How many times have we all stopped at a traffic light, the familiar shape and position of those colors so burned into our brains that we hardly even see them anymore? If you feel that way, maybe you should wonder what would happen if those colors suddenly disappeared, and we had to rely on our memories to determine which position told us to go, and which one told us to stop.
Needless to say, the three separate colors in a traffic light are extremely important. Besides their designations as stop, slow down, and go, the colors are also important from a design perspective. The traffic light was designed with three very different colors--red, yellow, and green. It is important that each of these colors comes with a distinctive hue because of the changing nature of colors based on their surroundings.
When viewed from a different angle, or with sunlight reflecting upon them, colors can sometimes appear as almost completely different shades. If red had been orange instead, in bright sunlight, a driver could possibly mistake a stop light as a yield light, and run the light, creating a dangerous situation for themselves and drivers around them. It is also important that the value of each color is light enough that the colors do not blend into the black around them, but shine in sharp contrast, alerting drivers of their presence.