Green, where top leaves turn red (4)
I believe the answer is:
lush
'green' is the definition.
(I've seen this in another clue)
'top leaves turn red' is the wordplay.
'top' says to take the initial letters (in a down clue, the first letter is top).
'turn red' becomes 'ush' (I am not sure about this - if you are sure you should believe this answer much more).
The initial letter of 'leaves' is 'l'.
'l'+'ush'='LUSH'
'where' is the link.
Can you help me to learn more?
(Other definitions for lush that I've seen before include "Lavish - boozer" , "dipsomaniac?" , "Succulent - soak" , "Of growth, profuse and abundant" , "Luxuriant (vegetation)" .)