Rank in Judo judo association. For a rank to be recognized, it must be registered with the national judo organization or the Kōdōkan. In Japan, the use of belt colors is related to the age of the student. Some clubs will only have black and white, others will include a brown belt for advanced kyū grades and at the elementary school level it is common to see a green belt for intermediate levels. In Europe the belt system is white, yellow, orange, green, blue, brown and black for both senior and junior practitioners. Judokas who have attained the 6th Dan may also use
Gardner color scale the liquid. This procedure isn't extremely accurate due to variations of observers, illumination and to some extent the standards themselves. Gardner Color can also be measured by a dual beam xenon flash spectrophotometer, for example the ColorQuest XT. Spectrophotometers measure the percent transmittance of the product and automatically calculate and provide the Gardner color number using illuminant C and 2º observer. Gardner color scale Gardner Color Scale is a one-dimensional scale to measure the shade of the color yellow. Colors of transparent liquids have been studied visually since the early 19th century. Changes in color can indicate contamination or impurities