In fact, the use of these three colors for traffic signals and human visual function structure and psychological response.
Our retina contains rods and three kinds of cone-shaped photoreceptor cells. The rods are particularly sensitive to yellow light, and three of cones are most sensitive to red, green, and blue light respectively. Because of this visual structure, people can easily distinguish between red and green. Although yellow and blue are also easy to distinguish, but because the eyeball, the blue light sensitive photoreceptor cells are less, so distinguish the color, or red, green is preferred. Therefore, the traffic lights with what color is also a scholar!
Color also has the meaning of activity, to express heat or acuteness, the strongest is red, followed by yellow. Green has a colder and calmer meaning. Therefore, people often represent danger in red, yellow for vigilance, and green for safety.
Moreover, because of the strongest penetration of red light, the other colors are easy to scatter, in foggy days is not easy to see, and red is not easy to scatter, even if the visibility of the air is relatively low, it is easy to see, there will be no accident. So we use red to indicate prohibition.