Silver filling is also known as amalgam and it just made with a metal alloy which expands and contracts with heat or cold.
White fillings are made with glass polymer and plastic also known as composite. The substance the cavity is filled with is almost the same color as the teeth. Unlike silver filling which has colors that contrast with the color of the teeth, White fillings blend in well with the teeth. The color is similar to that of the teeth, thereby giving you a more natural look.