Crossword Genius

Like carpet that's threadbare, missing underlay -- and yellow (6)

Ross

I believe the answer is:

naples

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

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

Can you help me to learn more?

(Other definitions for naples that I've seen before include "Major Italian city south of Rome" , "City near Mt. Vesuvius" , "Mediterranean city" , "Planes go awry in Italian port" , "Planes (anag) - somewhere in Italy" .)

I've seen this clue in The Telegraph.
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