Vivid red (7)
I believe the answer is:
scarlet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vivid red</span>' is the definition.<br/ ><span class="explanation-format__explanation">(scarlet is a shade of red)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for scarlet that I've seen before include "Let cars be this colour" , "bloody?" , "Fallen" , "Miss O'Hara appearing briefly" , "Brilliant red colour" .)