Brown tone (5)
I believe the answer is:
sepia
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">brown tone</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)