The official WCAG 2.1 – 1.4.11 Non-text Contrast (Level AA) Guideline states:
“People with low vision often have difficulty perceiving graphics that have insufficient contrast. This can be exacerbated if the person has a color vision deficiency that lowers the contrast even further. Providing a relative luminance (lightness difference) of 3:1 or greater can make these items more distinguishable when the person does not see a full range of colors.”
WHAT IS LOW VISION?
Low vision is the term used to describe significant visual impairment that can’t be corrected fully with glasses, contact lenses, medication or eye surgery. [SOURCE]
More from the W3C:
“Low contrast controls are more difficult to perceive, and may be completely missed by people with a visual impairment. Similarly, if a graphic is needed to understand the content or functionality of the webpage then it should be perceivable by people with low vision or other impairments without the need for contrast-enhancing assistive technology.”
TRANSLATION: When you follow this color contrast guideline, it assists people with low vision so they can more easily recognize icons and graphical objects on a web page.
Here are some examples:
Three check mark icon graphics appear below. Each one uses a different green color on top of a white background.
The icon on the left (light green #6cbf7e) has a failing contrast ratio of 2.29:1.
The icon in the middle (darker green #469156) has a passing contrast ratio of 3.86:1.
The icon on the right (even darker green #487651) has a passing contrast ratio of 5.27:1.
If the icon helps the individual to perform an action on the web page, or to understand the content around it, then the graphic must meet the minimum color contrast requirement of 3.1:1 so that folks with low vision can use it.
WEBSITE ACCESSIBILITY TESTING & REMEDIATION SERVICES: Mary Gillen is an experienced Website Accessibility Compliance Auditor and Remediator. She can test your website to determine if it meets accessibility standards:
WCAG 2.1: 312 checkpoints covering A, AA and AAA W3 accessibility guidelines
Section 508: 15 US federal guidelines covered by 59 accessibility checkpoints