Fossilised resin (5)
I believe the answer is:
amber
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">fossilised resin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for amber that I've seen before include "Cautionary colour" , "Cautionary signal" , "first light" , "Light colour between red and green" , ""Stop" traffic light" .)