Project Thumbnails Change On Rollover

I've read the how to on rollover states and fading and the custom HTML and CSS codes. And I've tried it all, but I can't seem to get it to work.

I want my project thumbnails to fade from B&W to color when you mouse over them. And change back to B&W when you move your mouse away.

I tried pasting in the HTML code and then the CSS and linking a hidden thumbnail image in. But nothing happens when I try to mouse over the thumbnail.

So, I'm obviously doing something wrong.