Color

Color scale begins with the letter D representing colorless and continues with increasing presence of color to the letter Z representing light yellow or brown. Each letter grade has a clearly defined range of color appearance. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.
Diamond color is all about what you can’t see – the less color, the higher their value.
The exception to this is fancy color diamonds such as pinks and blues, which lie outside this color range.