When deciding whether you want to use a plain color or an image you should consider the fact that very few of the web's 100 most visited sites use background images.
More than 90 percent have a plain white background.
The few pages that actually do use images use very discrete and fast loading images for the purpose.
When picking the desired color - whether it be plain or an image - you should also consider the fact that some colors work with almost any other color - while there are colors that only work with a limited number of contrasts.
If you use green on a red background, it will look different than if you use the same green on a blue background. Without digging into deep theories about colors, we will make a note on the fact that white, gray and black colors tend to be balanced against other colors. That is, white, gray and black work with any of the colors in the rainbow.
This is probably the reason that white, black and gray are the most widely used background colors found on the net.
If you're designing for a company that has a certain color they use in other graphics, it is very tempting to pick that same color for the background of the webpage. This might be a good idea, but there are other ways to emphasize a certain color than to use it as background for the page.
If, for example, you see a huge white wall with a bright red dot on it, which color makes the biggest impression on you? The 500 square feet of white or the one square foot of red?
The conclusion is, that limited use of colors often makes the appearence of the colors more powerful than if the entire page was one big painting.
Furthermore, when you limit your use of colors, you can use the colors more to underscore the navigation of the page. If secondary navigation elements are held in pale colors while primary elements are sharp - then the user will, by intuition, get the point.
You can read more about colors on webpages here.
Whether you want to add an image or a plain color as background you need to specify it in the <body> tag.
The following pages will teach you how.....