It's black during the auction, black (5)
I believe the answer is:
sable
'it's black' is the definition.
(sable is a kind of black)
'during the auction black' is the wordplay.
'during' is an insertion indicator.
'the auction' becomes 'sale' (I've seen this before).
'black' becomes 'b' (as in pencil classifications).
'sale' going around 'b' is 'SABLE'.
(Other definitions for sable that I've seen before include "Brush" , "Adventurous courage" , "(Fur from) small carnivore" , "Bales (anag.)" , "Black (heraldry); fur" .)