You'll find the code in header.php:
#page { background: url("/images/kubrickbg.jpg") repeat-y top; border: none; }This is very tricky since the sidebar light grey color is included in the same graphic as the left and right borders.
Sorry mom for getting all techie on you but it took me a while to figure this out and by posting it here I hope it helps others when they are trying out how to change the sidebar background on their WordPress blogs.
I'm working on a new Vlog Soup. Should be up later today.