Autumnal color (4)

I believe the answer is:

rust

(Other definitions for rust that I've seen before include "Reddish-brown oxide coating" , "A fungus; a corrosion" , "Reddish-brown coating formed on metal by moisture" , "Corrode" , "Reddish-brown coating formed on metal by damp" .)

I've seen this clue in The Wall Street Journal.

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