Grey not satisfied with girl's embrace (8)

I believe the answer is:

gunmetal

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'grey' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

'not satisfied with girl's embrace' is the wordplay.
'not satisfied with' becomes 'unmet' (I've seen this before).
'girl' becomes 'gal' (synonyms).
'embrace' is an insertion indicator.
'unmet' put within 'gal' is 'GUNMETAL'.

Can you help me to learn more?

(Another definition for gunmetal that I've seen is " sheeny colour".)

I've seen this clue in The Times.

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