That brown background is set in
sitesculptor_assets/content/css/content.css
#outerWrapper #topNavigation {
background-color: #FFFFFF;
background-image: url("../images/topNavigation_bg.png");
background-repeat: repeat-y;
color: #FFFFFF;
height: 30px;
padding: 8px 0 0 8px;
}
it is the mages/topNavigation_bg.png background image that is causing the brown banner.