Dreamwidth style system discussion

The reason your background only shows up below the header is that there's a background color set for the header (color_header_background on the Nevermore page). I can confirm thanks to a quirk of my browser that the page background is above the header as well, behind the navigation bar. You should be able to remove the color by removing the color setting for the header background in the wizard or overriding it in the CSS. (You'll notice background colors for the page title and subtitle texts are set there too.)