Help using Muse Lightbox Thumbnail States

Hi

Ive just started using Muse and I have a query on the Lightbox.

What I want to do is have the normal state as a mono image and then the rollover/active as normal colour image - is there an easy way i can do this? As it seems to be fairly limited as what you can alter for different states..I cant see a way of replacing image with a mono one.

Any help would be great

Thanks

Paul