Vivid red vehicle belonging to this compiler (7)
I believe the answer is:
carmine
'vivid red' is the definition.
(shade of red)
'vehicle belonging to this compiler' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'belonging to this compiler' becomes 'mine' (belonging to whoever compiled the crossword).
'car'+'mine'='CARMINE'
(Other definitions for carmine that I've seen before include "Crimson pigment" , "Vivid red colour" , "Bright red" .)