Sure. Go to "My Organization" (up top) and click the "Edit Settings" button, then the "Home Page" tab on the left. There are 5 banner images to choose from, or you can upload your own image - but make sure it the right size/dimensions ( 960 pixels wide by 180 pixels high) or it gets stretched.
The background can't be changed at this time. It's something we're considering for the future, however.
Thanks,
Mike