Colour of old photographs (5)
I believe the answer is:
sepia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">colour of old photographs</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sepia that I've seen before include "Pigment got from cuttlefish ink" , "brownish colour" , "Reddish-brown colour - easy as pie" , "Brownish tint or pigment" , "Brown with a red tinge" .)