Color Perception Theories

Photoreceptors (rods and cones) enable light perception.
Humans perceive a rich range of colors despite having only three cone types: short, medium, and long wavelength.

Developed independently by Thomas Young (1802) and Hermann von Helmholtz (1850s).
Proposed before detailed knowledge of eye anatomy or photoreceptors.
Hypothesized three receptor types in the eye, each maximally sensitive to particular wavelengths (blue, green, red).
Input from these cones is integrated to perceive all other colors.
Analogous to mixing paints or light to create new colors.
The theory accurately predicted the existence of three cone types, later confirmed.

The trichromatic theory accounts for color perception deficits in individuals missing one or more cone types (color blindness).

Trichromatic theory cannot explain certain phenomena like color afterimages.
Experiment: Staring at a yellow and red image creates a blue and green afterimage.
The question of why staring at yellow leads to perceiving blue, and staring at red leads to perceiving green, remains unanswered by trichromatic theory.

Proposed by physiologist Hering as an alternative theory.
Suggests all colors are derived from three antagonistic color systems:
- Black and white.
- Blue and yellow.
- Red and green.
Fatiguing the blue-yellow system by staring at yellow results in perceiving blue when the yellow color is removed.
Fatiguing the red-green system by staring at red results in perceiving green when the red color is removed.
Successfully explains color afterimages.

Both trichromatic and opponent process theories are valid but operate at different stages.
Trichromatic theory applies to the retina, where three cone types exist.
Opponent process theory applies to later stages of visual processing in the brain's visual centers.