Blue dressing is cut off (6)
I believe the answer is:
Here is my best explanation:
'cut off' is the definition.
'blue dressing is' is the subsidiary indication.
'blue' becomes 'down' (I've seen this before).
'dressing' is an insertion indicator (a dressing is a kind of covering).
'down' placed around 'is' is 'disown'.
(Other definitions for disown that I've seen before include "Disinherit or repudiate", "Repudiate - disinherit", "Disinherit or renounce", "Repudiate, cast off", "Refuse responsibility for", "Forsake", "Refuse to be associated with (a person)", "Reject all connection with, refuse to acknowledge", "Refuse to acknowledge a connection" and "Is down (anag)".)