Brownish colour of a deteriorated silver piece (5)
I believe the answer is:
liver
'piece' is the definition.
(liver is a kind of piece)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for liver that I've seen before include "Internal organ" , "Bodily organ" , "Human organ" , "Abdominal organ" , "Large organ in the abdomen secreting bile" .)