Styling tags of custom posts

Hi,
I have been trying to style my tags.
Here is my code

<?php $terms = get_terms( 'portfolio_tag' ); ?>
<?php $tags = wp_get_post_terms($post->ID, 'portfolio_tag');?>

Here I retrieve $terms, the list of my tags for portfolio and $tags, the tags for the post.
Now, I wanted to display the whole list and put a color to the ones of the post.

<?php foreach ($terms as $term ) : ?>
<li><a href="<?php bloginfo('url'); ?>/portfolio-tag/<?php echo $term->slug ; ?>"><span><?php echo $term->name; ?></span></a></li>
<?php endforeach; ?>

Within this list, I would like to indicate the ones which are displaying into the post
I know that I have to put the result of my query into the
<li> with <li class="<?php echo $result; ?>
But I am unable to create my query, Should I have to add an other foreach? and asking if $term->term_id = $tag->term_id then echo “yes”?
Thanks for your help
Mad