Bright blue (5)
I believe the answer is:
azure
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bright blue</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for azure that I've seen before include "Blue like the sky" , "Deep blue colour" , "tone perhaps" , "heraldic colour?" , "Cerulean" .)