Brown tone (5)
I believe the answer is:
sepia
'brown tone' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sepia that I've seen before include "Colour of old photographs" , "Brownish tone associated with old photographs" , "source of ink" , "Reddish-brown colour as in old photos" , "Old drawing" .)