Changing color photo to Black & White (BW)

On http://www.ibisal.com/ you can see a small portfolio, just under main menu with thumbnails and a piece of information about project.

I want to present a bw photo and on RollOver change it into color. There is only one photo in database, full color, it should be done using actionscript changing color into bw.

Is there a way to create mask or just dynamicly change colors of colorful photo to black & white one?