Accessibility
Some browsers and devices do not support colors. For these blind and colorblind users, Web content depending on colors can be unusable or difficult to use.
Either no colors should be specified (to invoke the browser's default colors), or both the background and all foreground colors (primarily the colors of plain text, unvisited links, hovered links, active links, and visited links) should be specified to avoid black on black or white on white effects.
Read more about this topic: Web Colours