I decided to do a little experiment to see what difference the colouring medium can make to an image. The four picture below are of the same image stamped or printed on different papers and then coloured with the associated medium. Clockwise from the top left we have Prismacolor pencils on Bristol paper, a pre-coloured digital image on Stamping Up Whisper White card stock, Copic markers on XPressIt blending card, and watercolour paints on cold pressed watercolour paper.
Have a play with the mediums you have in your collection, it's really quite interesting to see how different the end result can be. Don't forget to switch the paper too... although some mediums won't work well with certain papers, such as alcohol markers with watercolour paper, you can get great results by mixing and matching.