Brought up key colour (4)
I believe the answer is:
bred
'brought up' is the definition.
(I've seen this before)
'key colour' is the wordplay.
'key' becomes 'b' (eg B major, musical key**).
'colour' becomes 'red' (red is a kind of colour).
'b'+'red'='BRED'
(Other definitions for bred that I've seen before include "did produce issue" , "Gave rise to" , "Very (music)" , "Brought up (to behave in particular way)" , "Produced offspring" .)