October is the month for painted leaves. Their rich glow now flashes round the world. As fruits and leaves and the day itself acquire a bright tint just before they fall so the year near its setting. October is its sunset sky; November the later twilight.—”Autumnal Tints“
Nobody beats Henry David Thoreau at Autumnal quotes. I would argue that C.S. Lewis, L.M. Montgomery, and J.R.R. Tolkien have superb passages, but if you simply need a pithy autumnal quote about nature, Thoreau’s your man.