Still spoiler on rear of vehicle painted with coloured substance (3-3)
I believe the answer is:
red-eye
'still spoiler' is the definition.
(something which spoils photographs or stills)
'on rear of vehicle painted with coloured substance' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'rear of' suggests the final letters.
'painted with' means one lot of letters goes inside another (to paint can mean to cover).
'coloured substance' becomes 'dye'.
The final letter of 'vehicle' is 'e'.
'e' put into 'dye' is 'deye'.
're'+'deye'='RED-EYE'
(Other definitions for red-eye that I've seen before include "Poor quality, coarse powerful whiskey" , "Poor whiskey - overnight flight" .)