Pure gold is 24 Karat and is soft and not suitable for day to day use. To make it harder, jewelry making companies add impurities. They add silver, nickel, copper, zinc or palladium.
These impurities can change the color of the gold to pale yellow, tinted brown, pale rose, or reddish. Adding silver and palladium makes the gold pale yellow. It looks like white gold but not true white.
To make it truly white gold, jewelry makers use rhodium plating. A rhodium layer covers the surface of the jewelry item. That makes it white gold and also harder and more durable.
The downside is that the rhodium plating will wear off after some time. You will need to take it to a jeweler for rhodium plating again.
The purity of the white gold is expressed in Karats. White gold like other gold types can be 10K, 14K, 18K or higher.
White gold may contain nickel, which causes an allergic reaction for some people. In general, one out of eight people are allergic to nickel. If you are allergic to nickel you should make sure the piece of jewelry is nickel-free.