Abstinent — muted in colour (5)
I believe the answer is:
sober
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">abstinent</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">muted in colour</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for sober that I've seen before include "Snot drunk" , "Sedate and rational" , "Staid; clear-headed" , "Judge said to be so" , "Serious or solemn and not drunk" .)