White gold was created in the 1920s as a more affordable option for platinum. Modernly, it has become the second most popular color for gold, seconded only to yellow and followed closely by rose gold.
To make gold appear white, metal crafters will "bleach" it by adding nickel or palladium to the pure gold. More expensive varieties will then be plated in rhodium to give them an even whiter appearance.
White gold is not pure. White gold is a 14-karat variety, whereas higher-priced yellow gold is 24-karat.
Yellow gold can be comprised purely of gold, 24-karat or a lower quality 14-karat in which other metals are added in.
While yellow gold is initially changed into white gold, it is not usually feasible to change white gold back into yellow. For this transformation to occur, the gold would have to be melted and the other alloys removed.
White gold can be plated with yellow gold to give it a yellow appearance. This process is done by a plater.