A shade of caution (5)

I believe the answer is:

amber

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'a shade' is the definition.
(I know that amber is a type of yellow)

I can't explain the rest of the clue.

(Other definitions for amber that I've seen before include "Yellowish colour" , ""Stop" traffic light" , "Light colour between red and green" , "Light giving warning" , "Name of female" .)

I've seen this clue in The Irish Independent and The Globe and Mail.

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