Humans mainly see three colors. If you have worked with film or video, you know what the three colors are: red, green, and blue, often abbreviated collectively as RGB. All the other colors we talk about, purple, gold, gray, brown, and so on, are just combinations of these three colors.
It isn’t strictly true that humans see only three colors. We also have some ability to see infrared and ultraviolet and to distinguish different frequencies within the red, green, and blue bands. But those are distinctions we don’t really care about emotionally. That’s why it works so well to reduce an image to the red, green, and blue of a video screen. When we see the right proportions of red, green, and blue, we feel like we’re seeing the same color, even if it isn’t the same in any other respect.
Color theorists talk about red, green, and blue as if they were arbitrary and interchangeable. In one way of thinking, it is just an accident of human vision that these are the three colors we happen to see, but as long as that is the case, color is just a matter of mathematical measurements of these arbitrary color bands. And perhaps that is an accurate way of looking at it if you are designing a video display that shines red, green, and blue dots into an otherwise relatively dark room. But outdoors, in sunlight and in the natural environment, there is a very real difference between red, green, and blue. They are not arbitrary or interchangeable at all, nor are they the equivalent of each other. In fact, when you look at what the colors actually are, they are so different from each other in their nature and purpose that you will marvel that we are able to treat them as mathematical abstractions at all.
Looking at color in the light of the context and purpose of human vision, it is easy to see why there are three colors, why the three colors are specifically red, green, and blue, and what these colors mean, not just in relation to each other, but in relation to the human environment. This is the subject I will cover this week.