Fixed copper colour (5)
I believe the answer is:
cured
'fixed' is the definition.
(I've seen this in another clue)
'copper colour' is the wordplay.
'copper' becomes 'Cu' (Cu is the chemical symbol for copper).
'colour' becomes 'red' (red is a kind of colour).
'cu'+'red'='CURED'
(Other definitions for cured that I've seen before include "Remedied" , "Made well" , "Preserved by drying, salting or smoking" , "Successfully treated" , "Mended" .)