To enhance what drmike is saying, you are seeing the background color because the kubrick header has a white border wrapping the image and the slight fade you see through the content area.
Find the following (midway down the page):
margin: 0 0 0 1px;
#73a0c5 is the color you are seeing, but changing the color to #fff isn't going to fix your problem. Instead of blue, the color will then be white. Test my theory, by setting the above 'background-color: ' to #000. It's will be black, and ugly.
If I were you, take the kubrick header img and place your current header over the blue gradient portion of the image, leaving the white border and the slight fade. This will be the easiest fix.