You're fighting the elements. You want color but the sky is white. That's a tough battle. Shoot a colorful sky, and then enhance. You can use white balance tricks, like shooting in tungsten on a cloudy day or white balancing off colored gels. Or set the WB to cloudy for a bit more warmth. Also the wheel shots are top lit, meaning the underside of the cars is in shadow. That shot might be better taken at night when the lights provide interest. Also, use a polarizer to cut haze and reflections and enhance contrast and saturation.