Pale green used by teenage Auden illegibly (3,2,3)
I believe the answer is:
eau de nil
'pale green' is the definition.
(I've seen this before)
'used by teenage auden illegibly' is the wordplay.
'used by' indicates the answer is hidden within the clue.
'EAU DE NIL' is hidden within 'teenage auden illegibly'.
(Other definitions for eau de nil that I've seen before include "shade" , "Pale green colour" , "pale-green colour" , "Pale greenish colour" .)