Gem-quality diamonds occur in many hues. In the range from colorless to light yellow or light brown; diamonds are compared to Master Color-Comparison Diamonds under controlled conditions. Colorless diamonds are the most rare. Other natural colors are known as fancy — their color grading is unique. These small, subtle differences in color can make a substantial difference in value. If a diamond is well cut, its refraction and dispersion often will disguise certain degrees of coloration. Unless a diamond is a fancy color (or any color other than colorless to light yellow or brown), the American Gem Society™ Color Grading System places it on a 0 – 10 scale, with 0 being colorless. To accurately and consistently grade color, an American Gem Society Laboratories-trained grader will use special lighting to compare the diamond being graded to a set of American Gem Society Master Color Comparison Diamonds, which have met exacting standards of Cut, Color, Clarity, and Carat Weight.