I haven't done this in years, but I USED to get silicone crystals and put the leaves, flowers, in an airtight bag and gently pour the crystals all over the foliage. Let it sit in a dark place for a while (maybe a month) and then take them out. Seems like it was the best for preserving with out loosing too much color. Another thing, but it's not as easy is to put them in a mold and pour epoxy over them. Makes like a paper weight thingy. But that ususally keeps the colors real nicely and it's definately FOR EVER!!!
Of course you can always IRON it between two pieces of wax paper!!! (be sure to put a plain piece of paper over the wax paper so you don't ruin your iron) That works too!!!
Post a pic! I love fall stuff!!!
Lynn