Accessible colours for WCAG 2.0 AA - Do vs Don't

Accessibility means that all people can perceive, understand, navigate, and interact with electronic information and be active, contributing members of the digital world. Visual, auditory, physical, speech, cognitive, and neurological disabilities should be taken into account when implementing accessibility measures.

More importantly Everyone benefits from accessibility. 

Accessible design improves access to information on the web for individuals with and without disabilities. Well-designed, accessible web sites expedite the delivery of information and services. Providing accessible websites and electronic documents allows a greater variety of consumers to obtain information regardless of their individual needs.