I did what you are describing. I have the Kubrick template and on my stylesheet.css, the change I needed to make was at the very top of the page, line 5, where it says “background” (I changed it to ededed from what it was before). In whole, it looks like this:
/* Begin Typography & Colors */
body {
font-size: 62.5%; /* Resets 1em to 10px */
font-family: ‘Lucida Grande’, Verdana, Arial, Sans-Serif;
background: #ededed url(‘images/kubrickbgcolor.jpg’);
color: black;
text-align: center;
}
This changed the area outside the container where the text is. The white background for the container is governed by the “page” part of the stylesheet.
Anyway, I hope that helps.