Black Aussie truck in Scottish island (4)
I believe the answer is:
bute
'scottish island' is the definition.
(I've seen this in other clues)
'black aussie truck' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'aussie truck' becomes 'ute' (Australian abbreviation for utility vehicle).
'b'+'ute'='BUTE'
'in' acts as a link.
(Other definitions for bute that I've seen before include "Scottish isle" , "The Kyles of - - (Clyde)" , "Island in the Firth of Clyde" , "Old PM" .)