how to make black and white thumbnails that change into full color?

Hi there,

I'd like to have a portfolio with black and white thumbnails, that change into full color when you roll over and when you click on them. My question is how to make this black and white state- I can't fild that sort of filter in Muse. Does this mean I have to use 2 images- one b&w and the other in color? How do I make this work?

hope you can help me...

thanks, Maja