Yellow gold is classic. Although in its purest form it is usually too soft for jewelry. Therefore, we add other metals and alloy it to make it hard enough to fashion into wearable jewelry. The type of metal alloyed with the gold will determine what color or tone the gold will be. There are all types of gold tones, the most popular being yellow but also white, pink or rose, green, and even blue.
Gold is measured in karat weight, often abbreviated kt or simply K. 24k is the purest form of gold being 100. There is also 18K = 75, 14K = 58.3, and 10K = 41.7.