Is there a way to change the background image of the header image area independently of adding that image to the header image itself?

I used the below bit of code in Overlayed Blog Title/Tagline Style, but nothing changed.

background: url(/blog/wp-content/themes/atahualpa/images/stained_glass.gif) repeat top left;

My site: http://sixdegreeswebdesign.com/blog/

Either add the full URL to the image or try

background: url(/wp-content/themes/atahualpa/images/stained_glass.gif) repeat top left;

I think blog shouldn't be there for the shortened URL