Your asphalt driveway needs to be seal coated. If it is not, the greying of your driveway will be an indicator of a major, yet often overlooked, issue: stone erosion. The stone in the asphalt will literally flake off and eventually wash away. This process destroys the surface of your driveway and exposes the core to water damage and eventually cracking. The base of the driveway might shift and, if the surface is not held together strongly, the driveway will fail and crack.
Seal coating your driveway helps to prevent crack development, crack expansion, erosion (stones coming up), and a grey or white appearance.