A bit of blue as sunset mist dispersed (10)

I believe the answer is:

smuttiness

'a bit of blue' is the definition.
(blue can mean indecency, obscenity or pornography)

'sunset mist dispersed' is the wordplay.
'dispersed' is an anagram indicator.
'sunset'+'mist'='sunsetmist'
'sunsetmist' is an anagram of 'SMUTTINESS'.

'as' is the link.

(Another definition for smuttiness that I've seen is " Mild indecency".)

I've seen this clue in The Telegraph.

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