The gold alloy containing nickel or palladium to create a white appearance is called white gold.
White gold is not a single fixed recipe. It is gold alloyed with one or more white metals, most commonly nickel or palladium; copper, silver, zinc and platinum may also be added. The mixture changes the alloy’s hardness, color, workability and durability. A common formulation is 90% gold and 10% nickel by mass.
Gold purity is still measured in karats, just as it is for yellow gold. Eighteen-karat white gold contains 75% gold, while 14-karat white gold contains about 58.3% gold. The remaining percentage consists of the alloying metals, so “white” describes the color family rather than a claim that the item is pure or naturally bright white.
Many white-gold jewelry pieces receive a very thin rhodium coating, which gives them a brighter, platinum-like surface. That coating can wear away with use. Nickel-containing versions can also cause nickel dermatitis, which is why palladium-based or other nickel-free alloys are preferred by some wearers.