Relating to sort of blue film about break-up of USSR (7)

I believe the answer is:

prussic

'relating to sort of blue' is the definition.
(I know that prussic is the attribute pertaining to Prussian blue)

'film about break-up of ussr' is the wordplay.
'film' becomes 'pic' (short for picture).
'about' indicates putting letters inside.
'break up of' indicates an anagram (I've seen 'break up' mean this).
'ussr' anagrammed gives 'russ'.
'pic' placed around 'russ' is 'PRUSSIC'.

(Another definition for prussic that I've seen is " acidic?".)

I've seen this clue in The Times.

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