Visually dull (4)
I believe the answer is:
drab
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">visually dull</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for drab that I've seen before include "Colourless like bard" , "Dreary and colourless" , "Grey or light brown cloth" , "Gloomy" , "Not cheering" .)