If you find images that you like and might have a use for later, save them to a disk. Remember that if you choose a dark background and light text, your text will not show if it's printed on paper. If you expect people to be printing your documents, use a dark text color. Background colors and images do not appear on printouts. If you choose a background pattern, you will probably have to change your text color.
Different browsers handle colors and backgrounds differently.
If you want your pages to work in many different environments, keep them simple.