Background Images

http://wordpress.org/support/topic/different-background-for-different-pages-on-my-website?replies=3

Check this out for how to do it without buying anything. That covers the overall page background.

The same applies for post classes. For example, twentyeleven uses:

<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>

which then outputs

<article id="post-762" class="post-762 post type-post status-publish format-standard hentry category-general tag-3-3 tag-release tag-wordpress">

in browser. The same concept applies as in the above link for using the classes. This would style the bg of individual post containers, rather than the whole page bg