Clear-sky color (4)
I believe the answer is:
blue
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">clear-sky color</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 blue that I've seen before include "down in the dumps" , "Sad; university sportsman" , "Miserable - cerulean" , "ball at snooker" , "This could be royal or navy" .)