On return metal coil yellow and grey (2,6,7)
I believe the answer is:
no spring chicken
'grey' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'on return metal coil yellow' is the wordplay.
'return' is a reversal indicator.
'metal coil' becomes 'spring' (I can't explain this - if you can you should give a lot more credence to this answer).
'yellow' becomes 'chicken' (as in cowardly).
'on' backwards is 'no'.
'no'+'spring'+'chicken'='NO SPRING CHICKEN'
'and' is the link.
Can you help me to learn more?
(Other definitions for no spring chicken that I've seen before include "One who's seasoned" , "old?" , "not young any more" , "unseasoned meat, might you say?" , "Veteran" .)