So while I was taking a forestry class a few months ago we did something that I thought was pretty cool. We took leaves that had changed color (but had not fallen off the trees yet) along with from pine or cedar, layered them and transferred the color onto cloth. The image below is how mine turned out and the instructions along with what you will need are below that.
To complete this project you will need the following: cotton cloth (a clean, white flat sheet that is cut up works wonderfully and is easy on the budget), a hammer, wax paper, a piece of cardboard, the leaves/greenery along with a hard surface (we did this on a sidewalk).
Step 1: Layer the items as follow from the hard surface up (in other words from bottom to top):
-cardboard
-leaves/greenery
-cloth
-wax paper
Step 2: Using the hammer and some caution for your phalanges, smash the crap out of the leaves/greenery. Make sure you don't use the edge of the hammer or hit the hammer to the hard surface. This process takes several minutes and could be easily classified as a mini-workout. Make sure to get all of the surfaces of the leaves/greenery for the full effect.
Step 3: Check to make sure you got the image you wanted, if you want to add more then go right ahead. When you
carefully peel the cloth away from the leaves/greenery you will see that what you have left is pretty banged up and you might need some "fresh" leaves/greenery.
Step 4: Lay on flat surface to allow the material to dry overnight and either hang up or frame.
DO NOT WASH unless you plan on starting over!
So, what is happening here and why does this work so well? The science is basic, the leaves and greenery are an organic matter meaning they're made of cells. As the chlorophyll in the cells begins to break down we see these wonderful changes in color that makes fall so beautiful. As you smash the leaves/greenery, you are smashing the cells into the cloth which is what causes the color transfer. Pretty cool, huh? Keep in mind since you are handling organic matter, the color pigmentation will change with time, but still look pretty cool. Oh, and if you use pine or cedar, you will also transfer the oils from the needles onto the cloth causing it to smell of their parent cell.