Have you ever been confused by the terms white gold, green gold, and rose gold? All real gold is yellow, isn't it, so how do other colors fit in—are they imitations? They aren't imitations at at all--they are alloys, new metals that are created by combining two or more different metals.
Gold Alloys

Colored gold alloys are just as "real" as their golden colored counterparts. Pure gold is generally too soft to be used for jewelry, so other metals are nearly always added to it, no matter which color of gold is being prepped for jewelry making.
Chances are the ring on your finger is marked 18K, 14K, or 10K to indicate how much pure gold is present in the mix. The K stands for karat, the system used to state how much pure gold is found in an item.

Gold Karat Markings

24K gold is pure gold.
18K gold contains 18 parts gold and 6 parts of another metal(s), making it 75% gold.
14K gold contains 14 parts gold and 10 parts of another metal(s), making it 58.3% gold.
12K gold contains 12 parts gold and 12 parts of another metal(s), making it 50% gold.
10K gold contains 10 parts gold and 14 parts another metal(s), making it 41.7% gold. 10K gold is the minimum karat designation that can still be called gold in the US.
Even 18K gold, with its 6 parts of another metal, gives jewelers the opportunity to play around with color.

White Gold Alloys

Nickel can be mixed with gold to create a white (or gray) color; it can cause dermatitis in people who are sensitive to nickel.
Palladium is another metal used to create white gold alloys. Related to platinum, it is more expensive than nickel, but is less likely to cause allergic reactions than nickel.
Rose & Pink Gold Alloys

Copper is added to make gold-colored alloys, but additional copper creates pink and rose tones -- the more copper, the deeper the effect.
Green Gold Alloys

Greenish shades are created by adding silver to gold.
Black Hills Gold

Black Hills Gold jewelry is a good example of colored gold alloys. Most Black Hills Gold jewelry uses 10K or 12K gold alloys in shades of yellow, pink, rose, and green. The photo on this page illustrates a few examples of this colorful gold jewelry.
Making alloys isn't as simple as it might sound. Before they make an alloy, metallurgists have to consider how the metals will react with each other. Adding too much of one metal or another can make the mixture brittle, too hard, or difficult to work with. Some ingredients could make the mix too soft.

Metallurgists fine-tune their recipes to produce combinations that are attractive, durable and can be successfully worked into pieces of jewelry.