Black is black in retail event (5)
I believe the answer is:
sable
'black' is the definition.
(heraldic term for black)
'black in retail event' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'in' indicates putting letters inside.
'retail event' becomes 'sale' (I've seen this in another clue).
'b' inserted into 'sale' is 'SABLE'.
'is' acts as a link.
(Other definitions for sable that I've seen before include "Literary black" , "Bales of precious fur" , "Black; antelope" , "Black (heraldry); fur" , "Marten's fur - dark black" .)