A lot of people think that silhouettes are usually black black, but I've found that doing some tone on tone stamping creates a very lovely silhouette effect that is more subtle. This is what I've done for my MWM card. I stamped the silhouette flowers on the kraft cardstock with a Versamark pad to create a watermark effect. This same effect can be done without a Versamark pad as well. You just need ink and paper that are the same color!
I hope you take some time to play around with the silhouette images you have in your stash. If you make something you like, I hope you link it up in the original challenge post! HUGS and happy stamping, friends! :)