Livery? It’s back in cheap supply (7)
I believe the answer is:
hepatic
'livery?' is the definition.
(I've seen this before)
'it's back in cheap supply' is the wordplay.
'it's' becomes 'it' (I've seen this in other clues**).
'back' is a reversal indicator.
'in' is an insertion indicator.
'supply' is an anagram indicator (supply of letters to make).
'it' in reverse letter order is 'ti'.
'cheap' is an anagram of 'hepac'.
'ti' put within 'hepac' is 'HEPATIC'.
(Other definitions for hepatic that I've seen before include "Pertaining to, or affecting, the liver or liverwort" , "brownish-red" , "Relating to the liver" , "Livery" , "of an organ" .)