“In this discussion the names of colors — “red”, “green”, “blue” and so on — will be reserved for the color sensation we have when we look at the world around us. In short, only our eyes can categorize the color of objects; spectrophotometers cannot. This point is not a trivial one because many people viewing some of our experiments for the first time will identify something as being red or green but will then ask, as if their eyes were being fooled. “What color is it really?” The answer is that the eye is not being fooled. It is functioning exactly as it must with involuntary reliability to see constant colors in a world illuminated by shifting and unpredictable fluxes of radiant energy.”