Diamonds that are made up of 100% pure carbon (without any impurities) are completely colorless. However, almost all diamonds contain a certain degree of color “dirt” caused by traces of nitrogen, boron, hydrogen and other elements.
Most valuable diamonds have the smallest amount of dirt. There is, however, a class of diamonds known as color diamonds (or fancy diamonds) that are really colorful, ranging from blue, pink, yellow, green and more.
The color of diamonds is evaluated on a scale from D (colorless) to Z (bright yellow or brownish). Evaluating color diamonds has other rules (see below).