[@akapope Participant 11 years, 6 months ago]

Thanks for the help guys 🙂

I figured it out, but thought I would update in case anyone comes across this as well. I admit this may not be the best solution; however it is working and I am happy.

In the /wp-includes/post-template.php file, at line 427 I edited it to this:

if ( is_single() ) {
		$post_id = $wp_query->get_queried_object_id();
		$post = $wp_query->get_queried_object();
		$parent_id = get_post($post_id)->post_parent;

		$classes[] = 'single';
		if ( isset( $post->post_type ) ) {
			$classes[] = 'single-' . sanitize_html_class($post->post_type, $post_id);
			$classes[] = 'postid-' . $post_id;
			$classes[] = 'parentforum-' . $parent_id;

Where $parent_id = get_post($post_id)->post_parent;
And $classes[] = 'parentforum-' .$parent_id;

Are the additions.

Then in the themes /style.css file I added something like:

.parentforum-17,
.postid-17 {
background: #000000 url(http://alysiaworld.com/wp-content/uploads/2013/06/alysiasea.jpg) center top no-repeat fixed;
}

Boom Baby!