While pure gold is yellow in color, gold can also appear to have other colors. These colors are generally obtained by alloying gold with other elements in various proportions.

For example, alloys which are mixed 14 parts gold to 10 parts alloy create 14 carat gold, 18 parts gold to 6 parts alloy creates 18 carat, and so on. This is often expressed as the result of the ratio, ie: 14/24 equals 0.585 (rounded off), and 18/24 is 0.750. There are hundreds of possible alloys and mixtures possible, but in general the addition of silver will color gold green, and the addition of copper will color it red. A mix of around 50/50 copper and silver gives the range of yellow gold alloys the public is accustomed to seeing in the marketplace.

White gold

White gold's properties vary depending on the metals and proportions used. As a result, white gold alloys can be used for different purposes; while a nickel alloy is hard and strong, and therefore good for rings and pins, gold-palladium alloys are soft, pliable and good for white gold gemstone settings, sometimes with other metals like copper, silver, and platinum for weight and durability, although this often requires specialized goldsmiths. Almost all white gold jewelry is rhodium plated since gold alloyed with palladium or nickel never comes out true white, but tinted brown, therefore requiring a thin layer of rhodium to mask the tinted shade and make it true white.

Contact allergy

About one person in eight has a mild allergic reaction to the nickel in some white gold alloys when worn over long periods of time. A typical reaction is a minor skin rash. White gold alloys made without nickel are less likely to be allergenic.

Rose, red, and pink gold

For: Toona ciliata Rose gold is a gold and copper alloy widely used for specialized jewelry due to its reddish color. It is also known as pink gold and red gold. As it was popular in Russia at the beginning of the nineteenth century, it is also known as Russian gold, although this term has become somewhat rare.

Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content–the higher the copper content, the stronger the red coloration, as pure gold is yellow and pure copper is reddish. A common alloy for rose gold is 75% gold and 25% copper by mass (18 carat). Since rose gold is an alloy, there is therefore no such thing as "pure rose gold".

Rose gold alloys

The highest carat version of rose gold is also known as crown gold, which is 22 carat. As said in the previous paragraph, 18 carat rose gold may be made of 25% copper and 75% gold. For 18 carat rose gold, typically about 4% silver is added to the 75% gold and 21% copper to give a rose color. 14 carat red gold is often found in the Middle East and contains 41.67% copper.