It does take time! I did another test inside. I got the fabric very wet and thinned the paint a bunch. I used yellow and blue and then kind of mixed it at the edge for green. Yellow can get so dark that it does not lighten as much as the other colors under the leaves etc.
I put it under a lamp to see if that would work, but it did not make much difference. I then used a hair dryer on high. That did work, so I know that heat and light are both important. I did use some of the window clings, and even though there was a clear edge, the color displacement was the same. I think I really want to do this outside in the sun and heat. I'll keep gathering items to use.