Color Perception

This document is a second 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.

Color Perception Impact on Low Vision

Certain colors can be difficult to perceive by people with low vision. However, loss of color perception alone does not mean a person has low vision.

Incidence of Color Disabilities

Globally, 1 in 12 men (8%) and 1 in 200 women suffer from color disabilities. [colourblindawareness.org] Red-green disability is the most common form. It affects 7 to 10% of men and virtually no women. [colour-blindness.com] Blue-yellow disability affect males and females equally. It occurs in fewer than 1 in 10,000 people. [nhs.uk]

Types of Color Disabilities

Generally, 4 types of color disabilities exist due to the inability to see red, green, blue, or all color.

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

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

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

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 Examples

No color disability — Full color perception
(no disability)

Protanopia disability — Complete red-green disability
(protanopia)

Deuteranopia disability — Complete red-green disability
(deuteranopia)

Tritanopia disability — Complete blue- yellow disability
(tritanopia)

Achromatopsia disability — 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.