Diamond color is the second most important of the 4 C’s after Cut. The diamond color measures the absence of color. Much like pure water is colorless, a diamond formed without any chemical contamination or structural flaws is also colorless. But many diamonds have impurities that give them a hue, often a yellowish cast. This hue degrades the value of the diamond. In many cases, this imperfection is not noticeable or even visible. But it is measurable and affects the value of the stone.
GIA’s D to Z diamond grading scale measures the degree of colorlessness by comparing a diamond to a set of master stones with established color values.