French white is dull when finish becomes dead (5)

I believe the answer is:

blanc

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'french white' is the definition.
'blanc' can be an answer for 'white' (I've seen this before). I am not sure about the 'french' bit.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for blanc that I've seen is " (Of wine) white".)

I've seen this clue in The Irish Times.

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