It is important to keep in mind that the number of hardware/software combinations out there is bordering on the infinite. In particular, monitors vary tremendously in their colour responses. Be very careful when using unusual background colours and make sure that the contrast between text and background is sufficient. Light backgrounds and dark text are the easiest to read. Be aware that printers are often unable to print pages that have light text on a dark background.
And have pity on those with impaired vision.