How to achieve the following effect?

[millsloris]

If we open the following website - http://www.gazelle.com/ and mouse over the image, we see some effect on images (all images are grayed out and only one images is colored).How to achieve this? Is it jquery?I tried to investigate the code and the only think I see that there is only one image: http://m0-beta.gazelle.com/images/pages/index/main_stack_products.png.