Hello
To change the background to the article area of your template try adding the following to the Custom CSS field of your templates parameters...
#container_main .wrapper960 {background: #EEEEEE !important;}
Where #EEEEEE is your new background colour.
The top menu background is a single image which you can edit directly to your own taste. You will find this image located at ../templates/j51_resonate/images/header.png from the root of your Joomla installation (
http://demo.joomla51.com/0092/templates/j51_resonate/images/header.png).
CiarĂ¡n