Passed off as a dark suit (6)
I believe the answer is:
spades
'a dark suit' is the definition.
(I've seen this before)
'passed off' is the wordplay.
'off' is an anagram indicator.
'passed' is an anagram of 'SPADES'.
'as' acts as a link.
(Other definitions for spades that I've seen before include "dark suit" , "Does some groundwork" , "those getting soiled?" , "Implements for a suit" , "Card suits and shovels" .)