Colour of bream swimming (5)

I believe the answer is:

amber

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for amber that I've seen before include "Traffic-light colour" , "Yellowish colour" , "Colour of warning" , "Cautionary light" , "Prepare-to-stop signal" .)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app