body {
background: #C89C52 url(page_bg.jpg) repeat-x;
text-align: center;
font: 11px arial, sans-serif;
color: #E5D19C;
padding: 20px 0 0 0;
}
Change the "background:" attribute. The part after the hash is a color, the url points to an image to use for it. If you don't want a background image and just want a color then remove the url section, and change the color. Black is "#000000".