Colorblindness

Color Vision Deficiency (CVD), also called color blindness, 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.

Approximately 4.5% of the world population have some form of color blindness . In total, it affects 1 in 12 men and 1 in 200 women. These figures are higher for White people or others who have mixed race genes in their genetic history.  By the math, unless you work at a very small company, at least one of your co-workers is color blind.

What causes CVD?

CVD exists because some people don't have the ability 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.

Simplified human cone response curves.

• Dichromacy is what happens when one of the three cone types is missing or damaged.
  • 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 colorblindness, 5% of men). Deuteranopia is the total inability to see green (1% of men).
  • 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.
  • 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.)
• Monochromacy is what happens when two of the three types of cones are missing or damaged.
  • Achromatopsia is the extremely rare (1 in 33,000 people) form of colorblindness where there is no color, only monochromatic (shades of grey) vision.

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.

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.

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

There are even people who have CVD, but only in one eye, known as unilateral dichromacy.

As always, remember that you are not your user.

What people with CVD have to say

• Color Blind Probs is a Twitter account with a colorblind author who retweets problems other colorblind 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 colorblindness. Dan compares the challenges that each disability provides, and talks about how his son's struggles have helped him understand both disabilities better.
• Color Craft & Counterpoint: A Designer’s Life with Color Vision Deficiency by Noah Glushien on A List Apart -- Noah has a color vision deficiency and works as a designer and developer. He explains different aspects of colorblindness, and wants to set the record straight on a number of aspects of colorblindness and designing with color.

Design Considerations

Don't use color alone to communicate information. Ensure that your software passes WCAG Guideline 1.4.1 Use of Color

Tools

• Colorblind Web Page Filter by Toptal
• Check My Colours - will provide feedback on a color palette for colorblind users
• I Want To See Like The Color Blind - will provide colorblindness filters through Chrome.
• Color Oracle - a colorblindness simulator for Windows, Mac, and Linux
• Colorsafe provides accessible color palettes using a web tool

Colorblindness in animals

Can dogs see colors? on Colblindor

Sites with good design for people with CVD

• Our World in Data was recommended by Noah Glushien as a site that is designed well for everyone's vision, not just people with CVD.

Additional Resources

• Responding to Color by the Cooperative Extension Service of the University of Kentucky.
• Color Blind Awareness website provides information on colorblindness including types of colorblindness.