Small island turning black (5)
I believe the answer is:
sable
'black' is the definition.
(heraldic term for black)
'small island turning' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'island' becomes 'elba' (Italian island).
'turning' shows that the letters should be reversed in order.
'elba' backwards is 'able'.
's'+'able'='SABLE'
(Other definitions for sable that I've seen before include "Type of fur" , "North Asian marten" , "Bales of valuable Russian fur" , "Antelope, fur" , "fur coat" .)