Color reflected color depends upon the viewing angle. Numerous scientists have carried out research in butterfly wings and beetle shells, including Isaac Newton and Robert Hooke. Since 1942, electron micrography has been used, advancing the development of products that exploit structural color, such as "photonic" cosmetics. Color Color (American English), or colour (Commonwealth English), is the characteristic of human visual perception described through color "categories", with names such as red, orange, yellow, green, blue, or purple. This perception of color derives from the stimulation of cone cells in the human eye by electromagnetic radiation in the visible spectrum. Color categories and
Rank in Judo by the other organization. Advanced "kyū" levels can be earned by both seniors and juniors (children under the age of about 16) and are signified by wearing belts of various colours other than black. The order of belt colours can vary from dōjō to dōjō, depending on the dōjō's organizational affiliation. For senior players, both the United States Judo Federation (USJF) and ) the United States Judo Association (USJA) specify six "kyū", as listed in the table. The USJA requires "Beginners" (not a kyū) to wear a white belt until they test for yellow belt. The USJA also recommends wearing