Blue vehicle, turning over, last in rally (4)
I believe the answer is:
racy
'blue' is the definition.
('racy' can be a synonym of 'blue')
'vehicle turning over last in rally' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'turning over' says the letters should be written in reverse.
'last in' indicates one should take the final letters.
The last letter of 'rally' is 'y'.
'car' written backwards gives 'rac'.
'rac'+'y'='RACY'
(Other definitions for racy that I've seen before include "rather blue" , "bawdy quality" , "Spicy" , "Sexually suggestive" , "Suggestive, risque" .)