COLOR VISION

A. Basis: three subgroups of cones, one most sensitive to shorter visual wavelengths ("blue"), one most sensitive to longer wavelengths ("red"), and one most sensitive to intermediate wavelengths ("green")

Note: sensitivity depends upon absorption efficiency of each visual pigment

B. Trichromatic Theory: the color sensed depends upon the ratio of stimulation of the red, green, and blue cones

Examples:

Cones stimulated	Color sensed
Red only	Red
Red strongly, green less	Orange
Red and green equally	Yellow
Green mainly, less red and blue	Green
Blue mainly, less green	Blue
Blue only	Violet
Red and Green and Blue	White

C. Color Blindness and Color Weakness: absence of one or more types of cones will lead to color blindness for one group or all colors; reduced function of one or more types of cones will lead to color weakness

Example: absence of red-sensing cones will lead to red-green color blindness; absence of both red and blue cones will lead to total color blindness (monochromatic vision)