Blue vehicle overturning at end of motorway (4)
I believe the answer is:
racy
'blue' is the definition.
(I know that blue can be written as racy)
'vehicle overturning at end of motorway' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'overturning' is a reversal indicator.
'at end of' suggests the final letters.
The last letter of 'motorway' is 'y'.
'car' backwards is 'rac'.
'rac'+'y'='RACY'
(Other definitions for racy that I've seen before include "Slightly indecent" , "Suggestive, risque" , "Risqu" , "Lively" , "Suggestive; spirited" .)