Your are having background images in your website which must be preventing background color to display on whole page. Images always override colors. You can verify my point by disabling image loading in your browser and reloading it again (you might need to empty your cache first).
You can find image links throughout your style.css and remove them. Like this one -> url(images/footer-bg.gif)
Remember to make backup first.
Removing image link from
#site-generator {
background: url(images/footer-bg.gif) 0 bottom repeat-x;
border-top: 1px solid #ddd;
color: #999999;
font-size: 13px;
line-height: 1.6em;
padding: 1.8em 0.5em 2.5em 0.5em;
text-align: center;
}
should remove image from footer.
And from
body {
background: #e5e5e5 url(images/main_bg.png) 0 0 repeat-x;
}
should remove image from header.
notify if still having any issue.