The colour of old photographs (5)
I believe the answer is:
sepia
'the colour of old photographs' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sepia that I've seen before include "Sort of ink" , "source of ink" , "A greyish brown" , "Colourant" , "Reddish-brown colour as in old photos" .)