Trichromatic Theory

The eye is made up of four different types of light sensing cells:

• rods for black and white and
  
  
• cones for roughly red, green and blue (long, medium and short wavelengths)

This theory was developed by Thomas Young and Hermann von Helmholtz after having people adjust the intensity of a number of different colored light sources to reproduce a specified color. Young and Helmholtz saw that three different colored lights (color primaries) were required to match any color they could specify.

After Images Not Explained?

Some color researchers suggest that, although trichromatic theory is useful, it doesn't answer all color phenomena, afterimages, for example.

Stare at the red dot until the image goes away.

As you stare at the dot, fatigue of the retinal process occurs. When the image disappears, you see the complimentary colors.

We Think After Images Are Explained

We, however, believe that the trichromatic theory does provide an explanation for after images.

It is well known that a nerve that has fired requires additional time to recharge and fire again. What is less well known, or easily forgotten, is that the cones seem to adjust to various brightnesses over time and will fire periodically regardless of the level of light. (Have you ever see colors in the dark?)

After looking at a particular color for a period of time, that color cone is tired and fires less frequently then the other cones which have not been firing.

Opponent Process Theory

Although our eyes see color according to the trichromatic theory, our brain kicks in and uses the opponent process theory. It examines the relative strength of the cones using opponent pairs in this pattern:

• red vs. green
  
  
• blue vs. yellow
  
  
• light vs. dark  or  black vs. white (brightness)

Read more about the opponent process theory.