Like carpet that's threadbare, missing underlay -- and yellow (6)
I believe the answer is:
naples
'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" .)