Make sure you're not relying on color coding alone to convey information. Use of color is very useful and helpful, but it cannot be the only means of conveying information.
1.4.1 Use of Color: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element. (Level A)
Note: This success criterion addresses color perception specifically. Other forms of perception are covered in Guideline 1.3 including programmatic access to color and other visual presentation coding.
How to fix:
If your page relies solely on the use of color to convey information (for example, which fields in a form are required), add another means of conveying that information. For example, you could add an asterisk to each required field, or add some text at the beginning of the form indicating which fields are required, or use the HTML title attribute to indicate requirement. (HTML 5 adds a "required" attribute , but it may not yet be supported by assistive technology)