Hello,
You can control that by adjusting the background color below:
Template.CSS - Line 746
#s5_leftwhite, #s5_rightwhite {
background: #ffffff none repeat scroll 0 0;
height: 100%;
position: fixed;
top: 0;
width: 14px;
z-index: 1;
}
The body { background is what controls the rest of the white bars at the top/bottom/middle areas.