Yellow gold is an alloy of gold silver and some copper and there are other alloys of colored gold as well one of my favorites is blue gold which is an alloy of gold and indium. Red gold also called rose and pink gold depending on whom you ask is an alloy of gold and a much higher percentage
link of copper than yellow gold. Sometimes there's a touch of silver in there as well depending on how red you want your red gold to be
link but the alloy
link can be and often is just copper and gold.