I don't know how you would color them in that way.. but here's something..
have you tried the watercolor crayons? I use those often on my solid image stamps..
1. lightly mist your stamp with water (old spray bottle is what I use)
2. color your flowers directly on the stamp with the crayons.
3. lightly spray your paper OR lightly spray the paper
4. stamp..
creates beautiful images with flowers and such..
I have a few like this in my gallery if you want to take a look..
like
this
or
this