You can achieve the watercolour look in a variety of ways. Connie V. (from our card swap) used watercolours and a Julie Nuttig stamp - you can order it directly through Sandy.
Editted: February 7, 2016: Connie V.'s card image is currently out for publication. (Yeah Connie!)
Don't you love how Lorraine M. achieved this look with Tim Holtz distress inks?
And for the card below, I stamped with my Faber-Castell gelato to achieve the soft watery look of watercolours.
Have I inspired you to dabble with the watercolour look?