Bream changes colour (5)
I believe the answer is:
amber
'colour' is the definition.
(amber is a kind of colour)
'bream changes' is the wordplay.
'changes' is an anagram indicator.
'bream' anagrammed gives 'AMBER'.
(Other definitions for amber that I've seen before include "Warning to traffic" , "Road warning" , "Brownish yellow" , ""Stop" traffic light" , "Yellow, translucent fossil resin" .)