Many People think of diamonds as colorless. In reality, truely colorless diamonds are quite rare. Most Diamonds used in jewelry are nearly colorless with yellow or brown tints - most often light yellow.
Masterstones help you determine a diamond's depth of color and its place in the D-to-Z range. The same set can be used to judge yellow, brow, and gray diamonds in the normal color ranges.
Each masterstone represents the least amount of color in its range. A diamond with alightly less color than the H master stone is considered G-Color, one with slightly less color than the G masterstone is considered F-color, and so on. Fiave diamonds graded G can have five very slightly different amounts of color, but they all must have less color than the H masterstone, and more color than or an equal amount of color to the G. If a diamond has less color than an E masterstone, it's a D. This means there's no need for a D masterstone.