Pure gold is a soft metal and is most often alloyed with other metals to increase its durability and hardness. There are certain percentages of gold that are recognized as karats. The karat indicates the percentage of pure gold. 24kt gold is pure gold, therefore 18kt gold is 75% pure gold; the other 25% being other metals. Karated gold has a wide array of color that is determined by the other metals that are alloyed to create the karated gold.