I think if I was doing it, I would back baste one half of the leaf, leaving the extra where it goes under the other half. Applique it on, again leaving a little extra where it will be overlapped by the second fabric. Then I would continue with the other half of the leaf, folding the last half over the first half. Oh, gosh, I hope you understand this. I would only back baste one half of the leaf at a time if you want it two colors. I would think you could get a nice contrast in colors by a green material that had different variations in it. The pattern you are using is beautiful. Enjoy the process.