24-karat gold is 100% pure gold and pure gold is yellow in nature. In fact, gold and copper are the only metals that have natural colors. All other metals are white or grey in color.
In jewelry, there are various colors of gold including yellow gold, white gold, rose (pink) gold, and even blue gold. How does one make gold in colors other than yellow?
Remember that 24-karat gold can come only in yellow. However, when you decrease the purity of gold to 18-karat (75% pure gold), the remaining 6 karats has to be taken up by other metals that gives hardness, strength, and color to the gold. The combination of the pure gold and other metals is a gold alloy. There are numerous gold alloys that can be produced but the most common metals in gold alloys are: copper, silver, nickel, palladium, and platinum.
The table below lists the gold alloys that produce the colors you see in jewelry. Note that the word, "Silver" is interchangeable with nickel, palladium, and platinum which all have similar grey/silver color. Most commercial gold alloys are based on gold-nickel-silver-zinc alloys with copper often added to improve malleability. This copper addition, of course, affects color, and so such white gold alloys are not a good white color - more a slight yellow/ brown tint, particularly if nickel content is also low. As a consequence, such white gold jewelry is normally electroplated with rhodium (a platinum metal) which is tarnish resistant and imparts a good white colour.

