The colour of old photographs (5)
I believe the answer is:
sepia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">the 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 "Sort of ink" , "source of ink" , "A greyish brown" , "Colourant" , "Reddish-brown colour as in old photos" .)