Green's new leader embracing a bit of mystery (7)
I believe the answer is:
emerald
'green's' is the definition.
(I've seen this before)
'new leader embracing a bit of mystery' is the wordplay.
'new' indicates an anagram.
'embracing' means one lot of letters goes inside another.
'a bit of' says to take the initial letters.
The first letter of 'mystery' is 'm'.
'leader' anagrammed gives 'eerald'.
'eerald' placed around 'm' is 'EMERALD'.
(Other definitions for emerald that I've seen before include "Green gemstone" , "and 13 Across: Poetic name for Ireland" , "Highly-valued variety of beryl" , "Shade of green" , "La couleur" .)