John,
The background can be over ridden per domain as well. For the Customization you can use something like this.
<div
class="login-wrapper full-screen-bg-image"
style="width:100%; height:100%;
background-color: green;
z-index:-10;">.</div>
Example
Tony Scholz
System/Network Administrator
SmarterTools Inc.
www.smartertools.com