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
Judo rules Judo rules This article describes the rules of judo. The main sections of the article describe the rules that apply to any situation in which judo is practiced, and those rules which apply only in judo competitions. Separate sections describe the history of the rules of judo, provide links to other sources of information on judo rules, and list the references for this article. The scoring rules in use starting in 2017 are as follows: The following rules are no longer in use: Two types of penalties may be awarded. A "shido" (指導; literally "guidance" or "instruction") is awarded for