as in Sir Walter's eyes.

He's colour blind, and doesn't see the colour of Elizabeth's autumn. (sorry for digressing a bit, couldn't resist that.)

One other moment that's decidedly autumnal for me is when Anne leaves the room (CH3) after the discussion about who was to rent Kellynch.

Anne, who had been a most attentive listener to the whole, left the room, to seek the comfort of cool air for her flushed cheeks; and as she walked along a favourite grove,...

Groves and walking in them, with the thought of cool air bring pictures of autumnal paintings to my mind and I picture Ann walking in them.
The cool air blowing golden leaves down from the tree, and Ann in a pensive deep mood - "a few months more, and he, perhaps, may be walking here."