search for a custom field value in pots

hi every body,

How can i search for a custom field value in pots using URL, like this:
http://www.mywebsite.com/red-cars
red-cars are the custom field value
this is my idea :

<a href="<?php the_permalink() ?>/<?php echo $var_red-car; ?>">
Brows All the red cars
</a>

Thanks