Keep accessibility in mind when selecting colors. Contrast is extremely important for users with color blindness or visual impairments, so make it a priority to select font and background color combinations that pass accessibility tests.
The guidelines and Success Criteria are organized around the following four principles, which lay the foundation necessary for anyone to access and use Web content. Anyone who wants to use the Web must have content that is:
Perceivable - Information and user interface components must be presentable to users in ways they can perceive. This means that users must be able to perceive the information being presented (it can't be invisible to all of their senses).
This is the visual component of the guidelines and covers Text Alternatives, Captioning of Audio/Video Media, Adaptability of the Content and Presentation of Color & Contrast.
Operable - User interface components and navigation must be operable. This means that users must be able to operate the interface (the interface cannot require interaction that a user cannot perform)
This section involves Keyboard Accessibility, Timing of Presentations, Animation Requirements, Navigation Structure, and InPut Modalities (pointers, gestures, etc.)
Understandable - Information and the operation of user interface must be understandable. This means that users must be able to understand the information as well as the operation of the user interface (the content or operation cannot be beyond their understanding).
Information must be Readable, follow a Predictable & Consistent Navigation, and offer Input Assistance.
Robust - Content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. This means that users must be able to access the content as technologies advance (as technologies and user agents evolve, the content should remain accessible).
This involves website Compatibility with readers by accurate web programming.
If any of these are not true, users with disabilities will not be able to use the Web.