Grade d is almost colorless. Diamonds can have many colors besides being colorless and transparent. Colored diamond with jewel quality is called colored diamond. The colors of colored diamonds are yellow, green, blue, brown, pink, orange, red, black and purple. Colored diamond is rare, so its value is high, especially those with bright colors and high saturation are priceless. The most famous diamonds in history, such as Hope and Dresden, are rare diamonds with bright colors and high saturation. Color grading The color of diamonds is graded by colorimetry. In order to meet the needs of diamond trade, people have established the color classification of diamonds in long-term practice. Because colored diamond is extremely rare, there are some technical problems in actual operation, so there is no mature classification rule so far. Although different countries and regions adopt different color grading systems, these grading systems are similar to each other. The color grading system of American Gemological Institute divides the color of diamonds into 23 grades, which are represented by English letters D-Z respectively. The most commonly used one is 1 1 level d-n. The European color grading system retains strong traditional colors, represented by CIBJO. In the early days, colors were divided into six grades, and each color grade was described by words. In recent years, with the increase of trade between Europe and America, the two color scale systems tend to be consistent. China's diamond fineness grade basically draws lessons from foreign advanced experience. 1992 adopted the GIA classification of the United States when formulating industry standards. 1996 The newly formulated national standard integrates the advantages of GIA and CIBJO, and establishes the first color grade in China. The standard divides the colors into 12 grades, and uses D-N and < N. Diamond color grades D 100 extremely white E 99 F 98 excellent white G 97 H 96 white I 95 yellow white (brownish gray) J 94 K 93 light yellow (brownish gray) white L 92 M 9 1 light yellow (brownish gray)