Color Vision Deficiency (Colorblindness)

Color Vision Deficiency (CVD, formerly known as colorblindness) is a specific visual disability where the user may (or may not) be able to clearly see, but they are unable to fully perceive the color in what they see.

Note.
Many people with CVD prefer “CVD” to “Colorblind” because many people without CVD think that “Colorblind” is the same as “only sees black and white” and that’s rarely the case.

Approximately 4.5% of the world population have some form of CVD. It affects 1 in 12 men and 1 in 200 women. These figures are higher for white (Caucasian) people or others who have mixed race genes in their genetic history.  If your company is bigger than 20 people, there’s a strong chance at least one of your co-workers is color blind.

More than a few kinds of CVD exist, each with its own challenges.

  • Protanomaly is a reduced sensitivity to red light (1% of men). Protanopia is the total inability to see red (1% of men).
  • Deuteranomaly is a reduced sense of green light (and the most common form of CVD, 5% of men). Deuteranopia is the total inability to see green (1% of men).
  • Tritanomaly is a reduced sensitivity to blue light (and is extremely rare). Tritanopia is the total inability to see blue. (Put together they’re about 1 in 30,000-50,000 people.)
  • Achromatopsia is the extremely rare (1 in 33,000 people) form of colorblindness where there is no color, only monochromatic (shades of grey) vision.

People with either deuteranomaly or protanomaly are collectively known as red-green colorblind because regardless of which of the two types they have, they have difficulty distinguishing between red and greens, as well as browns and oranges.  They may also confuse blues and purples.

Design considerations

Don’t use color alone to communicate information. Ensure that your software passes WCAG 1.4.1 Use of Color – Level A

What people with colorblindness have to say about themselves

  • Color Blind Probs is a twitter account with a CVD author who retweets problems other CVD people have navigating the world.
  • On Smells and Colors by Dan Brown is about Dan’s inability to smell (called anosmia) and his son’s CVD. Dan compares the challenges that each disability provides, and talks about how his son’s struggles have helped him understand both disabilities better.

What causes CVD?

CVD occurs when a person is unable to detect light at certain wavelengths. 

Normal (human) vision uses three different cone cells in the eye to detect colors in specific light spectrums that roughly align to red, blue, and green light waves. If one or more of those cone types isn’t present or is malfunctioning, the affected light spectrum is affected. 

Normalised responsivity spectra of human cone cells from Wikipedia.
  • Dichromacy is what happens when one of the three cone types is missing or damaged. This includes those with protanomaly, protanopia, deuteranomaly, deuteranopia, tritanomaly, and tritanopia.
  • Monochromacy is what happens when two of the three types of cones are missing or damaged. It includes those with achromatopsia.

There are other people who have significant difficulty distinguishing red from black, making red-on-black or black-on-red combinations difficult to discern.

Some people have CVD, but only in one eye, known as unilateral dichromacy. 

For the vast majority of people, CVD was inherited from their mother. Others may become colorblind from other diseases such as Diabetes and Multiple Sclerosis, or from aging or certain medications. As many as 3% of the population could be affected by age-related deficiencies. Damage to the cerebral cortex of the brain could cause cerebral achromatopsia where people are aware of their visual experiences but are unable to imagine or remember colors. 

There are some people whose color vision is actually enhanced above normal. 

  • Tetrachromats have an extra set of cones that pick up more color between red and green than the usual trichromatic eyesight that most humans have.

Benefits of CVD

As with most disabilities, CVD is only a disability when the surrounding environment doesn’t align with a user’s experience. There are some benefits to CVD, according to Color Blindness or Color Vision Deficiency by Gianni A. Sarcone. 

  • The US Army has reported that people with CVD could better spot people or things in camouflage than those with normal color vision.
  • CVD may result in differences in texture or brightness more apparent. (The author posts an example picture on the page.)

Tools

Additional resources