I'm going to guess (after looking at the generated source) that you added the <div id="header_subscribe">...</div> after the %bar2 at ATO->Style & edit HEADER AREA->Style & edit HEADER AREA
By adding it there, it is it's own seperate element. %bar2 creates the horbar2 which is seperate from your new DIV
You need to add to ATO->Add HTME/CSS Inserts->CSS Inserts the following
HTML Code:
div#header_subscribe {
background:#FFCC66;
}
in addition you need to change the line '</div></center>' and make it '</center></div>' so you keep things in order