How can you make your top categories so when you are on there page (after you click them) they change colour?

its not using this menu but this site does what im talking about;
http://www.inksale.com/index.php?mai...index&cPath=32


When you are on the categories page the link goes turquoise blue. Whats also cool but probably harder is that the link stays a different colour when you are in one of its sub-categories.