Yellow gold is gold in its purest form. The purest yellow gold at 99.9 percent, 24 karats, is very soft and can be easily dented or scratched. Therefore, 22k, 14k, and 18k gold is infused with alloys to make the metal more durable.
White gold is produced when yellow gold is infused with silver, nickel or palladium. While yellow gold has been the most popular metal for wedding and engagement rings in history, white gold has proved far more popular in recent years. Yellow gold is alloyed with copper to make rose gold. The pinkish hue of rose gold has led to a huge bump in popularity because of its ability to complement all skin tones; yellow gold primarily compliments warm skin tones, and white gold compliments cool skin tones.