PatternSkinCssCookbook Recipe: Sidebar background color

#patternWrapper,
#patternSideBar {
 background-color:#eee;
}

This line loads the extra style definition:

   * Set USERSTYLEURL = %PUBURLPATH%/%SYSTEMWEB%/PatternSkinCssCookbookSidebarBackground/sidebar.css

You can write this line in DefaultPreferences, in SitePreferences, in WebPreferences, in your user topic, or on a single page.