One of the most common ways that the color changes and gold are observed is when different alloys are combined as inlays in jewelry where the lighter color of a particular alloy is used in conjunction with a darker colored alloy.
Although most interesting varieties of jewelry made this way is what is termed Black Hills Gold. Most of the jewelry made from this kind of gold is caret is carefully alloyed with other metals to create the colors.
Pink or rose gold is created by alloying copper with the gold causing it to acquire a pinkish or rose-colored caste. Another common alloy of gold creates a greenish caste by making an alloy containing silver.
Metallurgists will find them there recipes for different colors of gold. There is even a purple colored gold that is produced by alloying gold and aluminum.