Our group leader wasn't too specific with the measurements, she just put in a bunch of both in a bowl and mixed them together. The key is to make sure the consistancy is kind of stiff and solid, like stiff peaks when you're baking and mixing ingredients together. If you hold up the mixing spoon, the mixture should stay on your spoon and not fall off immediately.
Each child got a spoonful on their paper and then some dry powered tempura paint was sprinkled on top. She mixed it all up the colors combined. When the paint dried, it has a neat puffy texture to it. Just make sure you let it dry overnight, and only make as much as you think you'll use immediately. This paint does not keep.
I was thinking that if you did not have dry powered paint, you could add food coloring to the glue before mixing it together with the shaving cream to make it colored. Left white, this would be fun for winter snow projects. You could also sprinkle glitter in the pufffy paint to add some sparkle. I wonder if it would be thin enough to use in squeeze bottles. I was thinking that would be a fun way to paint with it. Imagine having your child trace over letters with it and then being able to feel the letters later. At any rate, the fun 3D texture when it dries is certainly fun to feel.