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Understanding color blindness

Color blindness is a common genetic condition in which some peoples' eyes can't tell the difference between certain colors. That's not to say these people see the world in greyscale— just that many colors seem identical to one another. Total color blindness is very rare in humans.

Color vision deficiencies (typically grouped together as "color blindness") are not rare. Some form of color blindness affects at least one in twenty people. Wikipedia has a helpful table, based on a journal article from There are several different forms of color blindness. The most common, red-green color blindness, affects around one in twelve men.

Color blindness is less profound than many impairments, but people with color vision problems often face restrictions on certain activities, which vary around the world. For example, Romania prohibits residents who are color blind from driving. The USA doesn't consider color blindness a disability because of workplace discrimination purposes.

Though there are multiple types of color blindness, they are the same in principle. For more information, check out Wikipedia's article on color blindness, which has some excellent descriptions.

What does this mean for accessibility on the web?

To make sure your site is readable for individuals with color blindness, avoid relying on color alone to communicate.

These guidelines are compliant with the WCAG; guideline 1.4.1 covers making content distinguishable using color.

In practice, you can achieve this by choosing colors that are easily distinguished from one another, and by adding secondary visualizations for icons and tasks. For example, say you're using red and green buttons to represent tasks a user has outstanding. It might seem logical to show items that need attention in red, and those that are good in green. One small change, such as overlaying a check mark icon over the "good" or "completed" items, will help communicate which items are approved and those that need attention.

There are cases where this isn't possible. The periodic table, for example, often color-codes the chemical symbols of the elements. When working with tables or other standardised layouts, adding more text or symbols might not be practical.

Available tools

There are a number of online tools to help those without color blindness visualize how accessible their designs are:

These tools are free, simple to use, and can quickly help you make color-accessible choices.

Terminology maintains a list of eye-related terminology, including links to additional resources.

This post was last updated on by Emily Lane.