Guardian boss goes after officer — factual accounts shouldn't be this! (8)
I believe the answer is:
coloured
'factual accounts shouldn't be this' is the definition.
(as in being coloured or distorted by a bias)
'guardian boss goes after officer' is the wordplay.
'guardian boss' becomes 'our ed' (the crossword setter's editor).
'goes after' means one lot of letters go next to another.
'officer' becomes 'col' (short for colonel).
'oured' after 'col' is 'COLOURED'.
(Other definitions for coloured that I've seen before include "It's not black or white" , "Rich in pigment" , "Tinted" , "Dyed" , "blushed" .)