Hi there, great question. The short answer is it's based on the combination of the aloy used. The long answer is that I have seen green gold too. It's all based on what you will be mixing in the metal alloy. The more percent of gold the less of other colors you will see. Different alloys are not just selected for color a lot of times it has to do with what you're trying to achieve softness of the metal hardness how flexible it is how durable is or how easily it can break. As per note online - An alloy is a mixture of chemical elements, which forms an impure substance (admixture) that retains the characteristics of a metal.