The most common form of color deficiency, red-green color deficiency, affects approximately 8% of the population. Using ONLY colors such as these (especially to indicate required fields in a form) will prevent these individuals from understanding your message.

Other groups of people with disabilities, particularly users with learning disabilities, benefit greatly from color when used to distinguish and organize your content.

To satisfy both groups, use color, but also be sure to use other visual indicators, such as an asterisk or question mark. Be sure to also distinguish blocks of content from one another using visual separation (such as whitespace or borders).

There are several tools you can use to evaluate color contrast, which will assist you in making your page as visually usable as possible to individuals with low vision or varying levels of color blindness.