Re: Painting a clear pickguard?
These made for plastic paints have a chemical that is essentially an adhesion promoter mixed into them. That doesn't change the fact that it doesn't get a great bond on baby-butt smooth plastic. Trust me, even with adhesion promoters and plastic paints, prep-work is required for painting plastics.
By all means, there is nothing stopping you from applying silver paint to the plastic. Be advised that the paint will be very prone to flaking and chipping. Additionally, be sure the paint is 110% cure before screwing it down to the guitar. If it's not, the silver paint could cure to the finish of the guitar. Assuming that bond would be much stronger than the bond the paint has with the plastic, the first time you try to remove the guard, the paint will peel off the guard and stay on the guitar's finish.