Pale blue colour (4)
I believe the answer is:
aqua
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pale blue colour</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 aqua that I've seen before include "Prefix denoting "water"" , "Tint of blue" , "Hue" , "Water; pale blue colour" , "Light bluish-green -- water" .)