Page template for 'checkout' and empty categories

Hi there,

I'm running MarketPress with the Atahualpa theme, and have problem finding how to style the background for checkout page and empty categories.
I have a dark background on the body, and a light background for pages and posts.

When I go to the checkout I get the same background as my body, and I get the shopping chart on top with links for archive and post categories down under it.

I started digging in Atahualpa settings, and there was it; an option for creating an 'archive' page. So I did, and the archive was gone from my checkout and empty categories. But the background is still dark..

Any pointers in what to do next?