Color Perception

This document is a first draft for the Color Perception section of the W3C WCAG Low Vision Task Force's Overview of Low Vision Wiki page. It is submitted in fulfillment of ACTION-18: Write first draft in plain English of color perception.

Specialized cells, known as cones that are located in the retina of the eye allow a person to see color. When these cells are absent or malfunctioning it can result in a decreased ability to see certain colors or a decreased ability to tell colors apart. Generally, 4 types of color disabilities exist due to the inability to see 1) red, 2) green, 3) blue, or 4) all color.

1. Red

Protanopia is the inability to see red light. People with protanopia have difficulty distinguishing green and red as they have an absence of L (red) cones. Red, orange and yellow brightness is reduced.

Simulated example of protanopia compared to full color perception

Protanopia disability — Example: complete green-red disability (protanopia)

No color disability — Example: full color perception

While protanopia is the inability to see red, protanomaly is reduced red sensitivity.

2. Green

Deuteranopia is the inability to see green light. People with deuteranopia have an absence of (green) M-cones. Protanopia and deuteranopia are similar in that red and green are confused.

Simulated example of deuteranopia compared to full color perception

Deuteranopia disability — Example: complete green-red disability (deuteranopia)

While deuteranopia is the inability to see green, deuteranomaly is reduced green sensitivity.

3. Blue

Tritanopia is an inability to see blue light. People with tritanopia have an absence of S-blue cones. They have difficulty distinguishing blue-green and yellow-violet.

Simulated example of tritanopia compared to full color perception

Tritanopia disability — Example: complete blue-green and yellow-violet disability (tritanopia)

While tritanopia is the inability to see blue, tritanomaly is reduced blue sensitivity.

4. No Color

Achromatopsia or monochromacy is the inability to see any color because of cones that do not work. People with these disabilities can only distinguish light, dark, and some shades of grey. This is rare.

Simulated example of achromatopsia compared to full color perception

Achromatopsia disability — Example: complete color disability (achromatopsia)

Color Simulators

User Needs

User needs related to color perception are addressed in the following section:

2.1 Luminance and Color - contrast adjacent, [color blindness needs?] Note: The term "colorblind" is frequently misleading as it seldom means a person sees in grey scale.