Highlight Anchor Links on Scroll?

[epfly]

Here's two examples that have navigation with exactly what Im looking for:
http://www.brizk.com
http://www.crushlovely.com

I've tried ripping the sites apart to figure out how they work and the most I can tell is that they both use a class called .current to change the background color as the page is scrolled down. Is this done via javascript? Can you provide some kind of sample so I can better understand how this is working? Is there a jQuery plug-in that does this?

A good explanation of how to implement would be greatly appreciated as I am mainly a CSS/HTML designer who is trying to learn more.

Thanks so much.

[KDLA]

It's a jquery accordion script. View the source, and look at <script type="text/javascript" src=".../wp-content/themes/brizk/_js/site.js"></script>