For finished diamonds, color, weight, clarity and cutting are common in the industry. It is called 4c rating. Color, in the color evaluation, we mainly classify the colorless-light yellow diamonds in Cape series. At present, the grading standards used are mainly based on the standards of CIBJO (International Jewelry Federation) and GIA (American Gemological Society) (that is, the color of diamonds is divided into 27 different grades by English letters D~Z, and the higher the letters, the higher the color grade of diamonds). However, confidence, the fifth C, was added as a reference. For example, the jeweler of Russia's ALROSA Elosa company also brings its own diamond certificate and diamond passport.