Make colourless (6)
I believe the answer is:
bleach
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">make colourless</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for bleach that I've seen before include "Chemically whiten" , "Make white or faded" , "Blanche" , "Go white" , "Get lighter" .)