The background is controlled by css, and can be viewed inside
css/style.css page. (Line 119)

body {
	margin: 0px;
	padding: 0px;
	* padding-top: 50px;
	* padding-bottom: 35px;
	background-image: url(../images/pageBackground.gif);
	text-align: center;
	font-family: Verdana, Arial, Helvetica, sans-serif;
    font-size: 11px;
}

To change the background can be done by inserting a new image or removing this line.
background-image: url(../images/pageBackground.gif);
and replacing that line with the code below

background-color:#FFFFFF;