Gold in its pure state comes in one color – yellow. However, when mixed with other metals gold can be come a variety of colors, the most common is white gold. White gold is usually a mixture of gold, copper, nickel, zinc and occasionally other metals. Even when these metals are added, white gold may have a yellowish cast, especially if it is 18K. The yellowish cast is not apparent when the jewelry piece is finished because the gold is covered with rhodium, a metal that gives it a hard bright white finish.
White gold tends to be harder than yellow gold, because it is mixed with other metals. Choosing white gold for a jewelry mounting will make the diamonds look icy white.