Copper colour is preserved (5)
I believe the answer is:
cured
'is preserved' is the definition.
(similar in meaning)
'copper colour' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'colour' becomes 'red' (red is a kind of colour).
'cu'+'red'='CURED'
(Other definitions for cured that I've seen before include "Made well" , "Of ham, smoked or salted" , "Preserved by drying, salting or smoking" , "Made healthy again" , "Healed or salted" .)