What exactly counts as incorporating the theme? Does the game's base story line have to be based on autumn?
i think the only that matter is that your game is set on autumn... and by that i mean the leaves of every single plant except pine trees must be orange...
Yeah pretty much this
could be set in an area with beautiful orange leaves, or incorporate pumpkins, spooky halloween skeletons, themes of autumn?
its a fairly vague theme that you can use to make whatever your creative mind comes up with :D
In books autumn often symbolizes change, maturity, beauty, sadness, and the beginning of the end
so there's alot of interesting themes to work with if you want to do something besides - orange leaf