Reddish-brown hue (4)

I believe the answer is:

rust

(Other definitions for rust that I've seen before include "deteriorate" , "Reddish-brown coating caused by oxidation" , "Reddish-brown coating formed on metal by moisture" , "Oxidised iron" , "Reddish-brown coating formed on iron by moisture" .)

I've seen this clue in the USA Today.

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