Mal de mer leaving maiden turning green (7)
I believe the answer is:
emerald
'green' is the definition.
(emerald is a shade of green)
'mal de mer leaving maiden turning' is the wordplay.
'leaving' suggests deleting specific letters.
'maiden' becomes 'm' (cricket abbreviation).
'turning' indicates an anagram.
'mal'+'de'+'mer'='maldemer'
'maldemer' with 'm' removed is 'aldemer'.
'aldemer' is an anagram of 'EMERALD'.
(Other definitions for emerald that I've seen before include "Mere lad (anag.)" , "Shade of green" , "Green gemstone" , "Ireland is often called The .......Isle" , "a type employed by the press" .)