Extend colors of header to screen edge using Drupal zen theme

How can I easily apply a bg image to only the gutter space between my header a开发者_开发百科nd the screen edge, using the zen theme? I am also interested in doing this for the footer as well.

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faced this creating this zen subtheme: http://mb.petrmarek.eu/

header: make a bg img for body

footer: easily define a custom region under the page wrapper and make a custom block for the footer