Give each post type label a different color?

You can do something like this:

<a href="https://wordpress.stackexchange.com/questions/80014/<?php echo get_post_type( $post->ID ); ?>" class="<?php echo str_replace(' ', '-', get_post_type( $post->ID )); ?>">
     <?php $post_type = get_post_type_object( get_post_type($post) ); echo $post_type->label ; ?>
</a>

and in your CSS part you can do something like:

.pretty-little-liars
{
   background color: khaki;
}

.once-upon-a-time
{
   background color: blue;    
}