Two or more elemental metals mixed to form a homogeneous mass are an alloy. Sometimes metals are alloyed with a non-metal such as carbon. The newly formed metal is usually harder, more durable, a different color and less malleable than the original components. Precious metal alloys remain precious as long as the precious metal dominates the mix and it is kept in certain proportions.
The Colors of Silver, Copper and Gold Alloys in Relation to their Composition.