This lets you style the comments for different roles.

 
<ol id="commentlist"> 
<?php foreach ($comments as $comment) : ?> 
<?php // The extra stuff to get commenter's role
$user_id = $comment->user_id; 
$role = ( isset( $roles[$user_id] ) ? $roles[$user_id] : '' ); 
?> 
<li> 
<p>By <?php comment_author_link() ?> - <?php comment_date() ?></p> 
<?php comment_text() ?> 
</li> 
<?php endforeach; ?> 
</ol> 

Add this to your style.css

 
#commentlist li { border:2px solid white; } /* not logged or subscriber */ 
#commentlist li.administrator { border:2px solid red } /* blog admin */ 
#commentlist li.editor { border:2px solid blue } /* editor */