…because I hadn’t, until about twenty seconds ago when I stumbled across this blog post. It looks like THE BEST THING EVER.
Apparently you steam-pressure real leaves onto paper so that their pigment is transferred onto the paper. Here’s Cassandra’s explanation:
OK — here’s how you steam under pressure. Big turkey roaster with a vegetable steamer placed on the bottom, and about an inch of water under that. I wrap the paper in a bundle with the leaves and cinch it tight with string. Place it on top of the vegetable steamer, weight it with three bricks, and let it steam for about two hours. You need good contact between the leaves and the paper.
It may be too late for pretty colored leaves here, but next Autumn this is top priority.