Here are 2 ideas using one mask and one of Lindsay's cool digi Sassy's, this one is Bubble Bath available here.
First print out the image on your chosen paper/card, and print a second copy on thin copier/zerox paper.
Using the copier copy cut an aperture mask as shown.
Colour your image as desired
Place the aperture mask over your coloured image and line it up.
Now stamp your fave stamp through the mask.
Here is the lovely result!
For the next idea, place the mask over some patterned paper, draw around the edges and cut out the paper.
Stick onto your bath for a diferent look. This technique for paper piecing is much easier and less wasteful than printing the whole image on your lovely designer papers.
Hope this is useful!
Thanks for looking.