The drying agent in common acidic silicones in the market is acid. Due to the active hydrogen, they have, acids immediately react with metals and darken the surface of the metal due to the active hydrogen they have. But the drying agent in neutral silicones is alcohol, which is Metals do not react.
On the other hand, acidic silicones can only stick to smooth surfaces, while neutral silicones can stick to porous and none porous surfaces.