Hello! I was wondering if there is any extension, or way to do that the gallery shows icons of the photos on black and white, and then when you press or put the mouse over it shows on colors. Like this website:
www.tonydorio.com

Hope this is possible. Please let me know.

Thanks

If it is possible is nearly always the wrong question :-) There is no extension for that. It could be done on modern browsers via CSS: http://demosthenes.info/blog/532/Convert-Images-To-Black-And-White-With-CSS
You would have to modifiying the CSS of the theme used.