Look at the Yale style manual for instructions for basic design principles. The color of the text and the background is chosen so that the text can be easily read. Avoid too much text and too tight layout. Most of the people want read the text on WWW-pages in small pieces. Avoid too many big and colorful pictures.
Pictures are nice, but the make the downloading of the pages slower.
The bigger and the more colorful pictures - the slower the downloading. If you have a set of pages, make sure that they share a common layout and a consistent menu system. Use common background, common colors etc. Navigation from one page to another should be as easy as possible. Animated pictures look funny, but they often disturbe, if you are trying to actually read the page.