Another idea......just bought a book called "Applique - The Basics & Beyond" by Janet Pitman. It has a project where you cut the leave motifs from a slightly darker shade of the background (like a tan) to give the illusion that these leaves are suspended in air. Then you position the darker shade under one side of the top leaf so it "peeks" out from one side. Add additional stitching for veins and it looks 3 dimensional.
It's a technique I'm going to try in making a small fall themed wall hanging. The book has some great hand and machine applique techniques and great patterns.
My friend keeps telling me about a tv show she saw about bleaching leaves onto fabric so that they seem like they are floating above the fabric. She is "positive" it was an Alex Anderson show, but they were unable to help so it's possible she is mistaken. Sorry I can't give more information. Hope someone can help.