I wondered if you could use water soluble makers to color the stamps too....  So I gave it a try!  These are just some washable markers from your local dollar store.

I hope I'm not making anyone cringe with my bad stamping!  Haha  ; )

I found that I really needed to add a lot of water to get the marker ink to behave like watercolor.  It still wasn't as nice as if I had used watercolors, I think.  But, it's fun!  : )