As well as the many color choosers which allow you to customize each element of your template, this template also allows you to edit the background image visible in the header, slideshow and bottom module positions from within your templates parameters.
Using the corresponding field under the Styling tab of your templates parameters hit the 'Select' button to access your Media Manager. From here you can upload the header background image of your choice directly from your computer. You can also remove this image and replace it with the color of your choice
It is also worth remembering that Joomla allows you to create multiple template styles which can then be applied to the menu items of your choice. This gives you full control of setting different backgrounds on different pages throughout your site.