I used this snippet of code to set a different css class or id based on the page template.

<div id="
<?php
if (is_page_template('template-home.php')){ echo "content-home";}
/*elseif (is_page_template('template-diff-bg-demo2.php')){ echo "template-diff-bg-demo2";}*/
else{ echo "content";}
?>
">

It could be modified to be conditional based on being the the home page as well.

Also note that is had to be put in the code/document as a single line for it to work…..don’t know why…….

<div id="<?php if (is_page_template('template-home.php')){ echo "content-home";} /*elseif (is_page_template('template-diff-bg-demo2.php')){ echo "template-diff-bg-demo2";}*/ else{ echo "content";} ?>">
 

This snippet is based on code taken from this article on the Fearless Flyer website:
http://fearlessflyer.com/2009/05/how-to-change-the-background-dynamically-in-your-wordpress-theme/