Red meal turns green (7)
I believe the answer is:
emerald
'green' is the definition.
(emerald is a shade of green)
'red meal turns' is the wordplay.
'turns' is an anagram indicator.
'red'+'meal'='redmeal'
'redmeal' is an anagram of 'EMERALD'.
(Other definitions for emerald that I've seen before include "Bright green colour" , "city in Oz?" , "and 1 Across: Ireland" , "Green gemstone" , "Green variety of beryl" .)