When we look at the world, we see a profusion of color: red roses, green grass, blue sky. It is easy to conclude that the real world is colored. This is just an illusion.

Consider a person locked in a windowless room with a computer screen connected to an outside video camera. The person can reorient the camera, "look" around the outside world and "see" it on the screen. This, of course, is just a processed image of the world. Were the person to open a window and look out, the real world would be directly visible. And it would differ from the processed image in many ways, such as the sublety of colors, the play of sunlight, the perception of depth. Locked in the room, the person has only an indirect view of the real world.

When we look at the world, we get the impression that we are seeing it directly, that we are looking out with our eyes and simply perceiving what is actually there. This is also an illusion. Our eyes do not look out, they take in. They take in patterns of light rays and focus them upon the retina; our optic nerve then relays this to the brain. The brain takes this data and processes it into an image on our visual cortex. Like the person in a closed room, we do not see the world directly, even though it appears to us that we do. We are locked in our own brains and what we "see" is a processed image on the visual cortex.

False color photography has become a common scientific tool. A satellite might image a ground area and provide the data to a computer. The computer will evaluatge the various wave lengths and provide a false color map. Wave lengths associated with vegetation might be shown as violet, plowed fields as rusty red, water as blue, even if it actually appears as green, brown or even black. The colors are not real. They are simply provided by the computer to give us an appreciation of the various land uses.

In the real world, objects reflect varying patterns of light waves. As humans evolved, they needed to sense these various patterns, to be able, for example, to rapidly find ripe fruit among leaves, or identify potential prey against a grassy background, or a potential predator against the same background. Our visual system does this for us. The rods in our retinas are sensitive to various wave lengths. The brain uses this data to paint an image on the visual cortex. So an object that reflects light with a 250 nanometer wavelength will be painted in as red. Grass, with a strong peak at 320 nanometer wave length, will be painted in as green. Our brains paint in these colors the same way that a computer paints in colors on a land use image. The colors that our brain paints are not in the real world any more than the colors the computer paints.

Color blind persons have visual systems that for one reason or another fail to recognize these different wave lengths. The black and white world which they see is a more accurate representation of the real world than the colored world most of us see. The vivid colors "around" us are not around us at all. They are only in our heads, painted by our brains onto the images in our visual cortex. Color is a creation of our brains. The real world is black and white.

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