Along the same lines of my previous post, I've been deconstructing the new default Dark Knight Skin for DotNetNuke.

Among other things, I couldn't figure out where that red shadowy / gradient image was coming from at the top of the page.

Didn't take me TOO long to realize that it was actually a solid red background color that was behind the semi-transparent background image:

    #Header #ContentBG{width:960px;margin:auto;background:#ff0000 url(images/Header-BG-Variable.png) no-repeat center bottom;}

Change that to the solid color that you want to peep through and you're all set.