Gossip about double blue (7)

I believe the answer is:

lowdown

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'gossip' is the definition.
The definition and answer are not the same part of speech.

'double blue' is the wordplay.
'double' becomes 'low' (I can't justify this - if you can you should believe this answer much more).
'blue' becomes 'down' (both can mean sad).
'low'+'down'='LOWDOWN'

'about' acts as a link.

Can you help me to learn more?

(Other definitions for lowdown that I've seen before include "news" , "confidential information" , "Data" , "Dope" , "facts" .)

I've seen this clue in The Irish Times.

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