A highly accessible web site uses web standards, which means XHTML and CSS. When using the W3C CSS validator to validate your CSS, many times the following warnings come up: “You have no color with your background-color” and “You have no background-color with your color”. In his blog posting, Roger Johansson explains why CSS Validator colour warnings are not errors. He states:
Those particular warnings are there for accessibility reasons and to remind you that you need to take care when specifying colours. The validator is trying to help you reduce the risk of your author stylesheets interfering with user stylesheets or system-wide colour settings.