There are 256 colors that are considered "web-safe."  These are basic colors, and all web browsers will render these colors the same.  If you would like a plain colored background for your web page, just tell me what color, the RGB numbers, or the "hex" code.
 

Most modern browsers will show custom colors correctly.  Each custom color hue and tint is given a RGB number which is rendered by the web browsers.  Older browsers may ignore the custom colors, and default to black (text) or white (backgrounds), or a web-safe color close to your choice..

Here are some good sites for choosing "contrasting and complimentary colors" which would be good for background as well as link colors.

A larger picture file may be used as a background, but this can occasionally make the text difficult to read.  See a sample page.

Another problem with fixed images has to do with screen resolution. If your monitor is set for 800 x 600 and the background is viewed on a higher resolution monitor, the background will tile. Or the reverse, where you create a background for a 1024 x 768 screen and someone views it on a 640 x 480 screen and will only see a small part of the image you want.

You should also keep in mind that a single background image may also take much longer to load than a repeated background tile.

Web page content is often placed in a  table with a colored background when the page background has a "busy" pattern.  Here is a sample web pages that uses a table background color for contrast and to help make the text readable.  My own personal webpage: 

A background tile is a small graphic file that is repeated over and over again on the web page to create a unified background.  If a tile is made correctly, it will appear seamless.  Background tiles are best if they have small prints or patterns that do not distract from the content.  The background tile for this page looks like this: