Color Scheme Designer
While designing color schemes for maximum readability is a topic best addressed in a graphic design-focused course on web design, Color Scheme Designer is a tool than can help you develop interesting and pleasing color schemes. The tool can export these color schemes for use in HTML and CSS or it can be configured to specify the colors in HTML Hex codes, RGB color space, or other formats, depending on the color-naming conventions you are following after reading about Color in CSS.
Like many web tools, Color Scheme Designer's usefulness will become apparent only if you experiment with the features built into its relatively simple design. Try to produce a few different pleasing color combinations and then apply them to elements of your example website using multiple, differently named external style sheets.