101

The trichromatic theory states that our cones allow us to see details in normal light conditions, as well as color. We have cones that respond preferentially, not exclusively, for red, green, and blue (Svaetichin, 1955). This trichromatic theory is not new; it dates back to the early 19th century (Young, 1802; Von Helmholtz, 1867). This theory, however, does not explain the odd effect that occurs when we look at a white wall after staring at a picture for around 30 seconds. Try this: stare at the image of the flag in Fig.10.2.1. for 30 seconds and then immediately look at a sheet of white paper or a wall. According to the trichromatic theory of color vision, you should see white when you do that. Is that what you experienced? As you can see, the trichromatic theory doesn’t explain the afterimage you just witnessed. This is where the opponent-process theory comes in (Hering, 1920). This theory states that our cones send information to retinal ganglion cells that respond to pairs of colors (red-green, blue-yellow, black-white). These specialized cells take information from the cones and compute the difference between the two colors—a process that explains why we cannot see reddish-green or bluish-yellow, as well as why we see afterimages. Color blindness can result from issues with the cones or retinal ganglion cells involved in color vision.

Reconciliation between these two theories lies in the retina. We have 3 kinds of photoreceptor pigments, but the circuitry of the retina combines them so ganglion cells respond along a red/green axis or along a blue/yellow axis.

Here are two Audiopedia videos on trichromatic theory and opponent process theory:

https://www.youtube.com/watch?v=boIp8Fi0WHQ

https://www.youtube.com/watch?v=8Wh5FJKPsKA