I borrowed the "Medallion" background stamp from my friend Gemma a couple of weeks ago and had a play with it. I cased the technique used here from the very talented Linda Higgins.
The technique involves stamping the Medallion stamp in Versa Mark. Then with your sponge daubers and pastels you dauber colour over the versa mark. Darker colours I found didn't work as well as they seemed to smudge. You only need to gentle dauber the colour.
Such an easy technique and makes a beautiful quick card.