Shade for small vehicle allowed (7)
I believe the answer is:
scarlet
'shade' is the definition.
(I know that scarlet is a human hair color)
'small vehicle allowed' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'vehicle' becomes 'car' (car is a kind of vehicle).
'allowed' becomes 'let' (to let is to allow or permit).
's'+'car'+'let'='SCARLET'
'for' acts as a link.
(Other definitions for scarlet that I've seen before include "Red colour of clarets" , "Let cars be this colour" , "Brilliant red colour" , "Fallen" , "Miss O'Hara appearing briefly" .)