Finishes off with single green layer (3)
I believe the answer is:
hen
'layer' is the definition.
(I've seen this in another clue)
'finishes off with single green' is the wordplay.
'finishes off' indicates one should take the final letters (take the finishing letters off of the words).
The last letters of 'with single green' are 'HEN'.
(Other definitions for hen that I've seen before include "Coop resident" , "Laying bird" , "Clucking female" , "Not cock" , "Domestic fowl" .)