Tuber skin color. With the help of the color chart for tubers (Fig. 11), determine the main or predominant color, from 1 to 9 (first digit), and the intensity of the same, from 1 to 3 (second digit); then observe the absence = 0 or presence = 1 to 9, of some secondary color as the case may be (third digit), if it exists, determine how the secondary color is distributed in the tuber skin, with the help of the scheme (Fig. 12) of distribution of the secondary color of the tuber (fourth digit). Four digits are read