Claro que no va a funcionar con eso, porque no entras en un vehiculo, cambia el modelo nada mas, usa esto: 
local colors = 
    { 
        { 128, 255, 0 }, 
        { 43, 25, 255 }, 
        { 255, 2, 255 }, 
        { 0, 255, 247 }, 
        { 201, 255, 0 }, 
        { 255, 0, 0 }, 
        { 0, 81, 255 }, 
        { 252, 255, 36 }, 
        { 87, 16, 154 }, 
        { 255, 94, 0 } 
    } 
  
addEventHandler ( 'onVehicleEnter', root, 
    function ( ) 
        setVehicleColor ( source, unpack ( colors[ math.random ( #colors ) ] ) ) 
    end 
) 
  
addEvent ( "onPlayerPickUpRacePickup", true ) 
addEventHandler ( "onPlayerPickUpRacePickup", root, 
    function ( pickupID, pickupType, vehicleModel ) 
        if ( pickupType == "vehiclechange" ) then 
            local theVehicle = getPedOccupiedVehicle ( source ) 
            setVehicleColor ( theVehicle, unpack ( colors[ math.random ( #colors ) ] ) ) 
        end 
    end 
)