A 'stop' sign often interpreted as 'go' (5)
I believe the answer is:
amber
'go' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for amber that I've seen before include "Yellow fossil-resin" , "Traffic-light colour" , "Prepare-to-stop signal" , "Colour of warning" , "Fossil resin used in jewellery" .)