Light beams start a series of reactions in the cells and sometimes the results continue after the triggering beams have gone. Most of us must take along a swatch of fabric when we go to buy a spool of matching thread. A few gifted people with color vision matching can guess a perfect match from memory.
Many people can remember colors, almost as if they were still seeing them. These and other special talents are rather rare and at present the biologists have no complete explanation of how they work. All of us, however, have experienced colors when we close our eyes after gazing at a colorful picture or pattern. Much, but not all, of this color Sensing in humans can be explained.
The basic color receptors in humans are light – sensitive cells called cones. There are about 130 million cones in the human eye behind the retina screen in the back of the eye. The human eye cones respond to the different wave lengths of light and flash their reactions along nerves to the brain’s center of vision. Part of the coding work needed to translate wave length into colors may or may not be done at the headquarters in the brain.
The most widely accepted modern theory on how this process is performed stresses the tendency of the vision to associate certain colors in pairs in humans. This pairing is evident in direct vision and also in the afterimage that appears when the eyelids are closed. In general the cones of the human eye tend to pair red and green and also yellow and blue.
There may be a factor of cell fatigue in the eye. When the human eye has been staring at a vivid color for a long time, it appears to fade and lose its brilliance. Color pairing and perhaps also cell fatigue seem to be responsible for colors that seem to appear on the inside of the eyelids of humans. One test for the after image uses a gray card adorned with a vivid green heart bordered in bright yellow. In the center of the heart is a black dot. The eye is allowed to stare at the picture for 2 seconds. Then it is replaced by a stark white card. For a moment, the eye may visualize the colored card. Then the afterimage changes to the paired opposites. It becomes a red head bordered with blue.
The modern theory suggests that certain cones in the eye handle the decoding of both reds and greens. Other cones deal with blues and yellows. When the triggering light waves are removed the electrical activity of the sensitive cone cells of the eye continues for a while.
Sometimes the same colors are sensed on the inside of the closed eyelids Sometimes an afterimage of the paired opposite colors is sensed In any case, the triggering action stops when the colors are removed from the field of vision. The stimulated cells of the eye however may continue to react to the colored wave lengths. Then we sense, rather than actually see colors with the eyes closed. Sometimes we can visualize colors and design them in imaginative patterns.
Emotions and other factors can stimulate colorful creations in the eyes of some. Some people have the gift to stimulate these artistic memories relating their color vision while asleep. They dream more colorful dreams.