There are probably several different ways to do this. I'm not aware of a plugin, but I think it would just be easier to figure out how you want to identify the posts as being unique and then assign them a class and style that class differently in your style.css file.
For example, if you wanted to style the posts by category you could do the following:
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
foreach((get_the_category()) as $cat)
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
<?php endwhile; else: ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>
This spits out the post's category slug as a class for each post's div. Having done that, then you can just set up your style sheet to style accordingly.
You can read more about get_the_category() here:
I don't have a way to test this to see if it actually worked, so let me know.