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
Orange (colour) a symbol of activity. Orange is sometimes used, like red and yellow, as a colour warning of possible danger or calling for caution. A skull against an orange background means a toxic substance or poison. In the colour system devised by the US Department of Homeland Security to measure the threat of terrorist attack, an orange level is second only to a red level. The US Manual on Uniform Traffic Control Devices specifies orange for use in temporary and construction signage. Because of its symbolic meaning as the orange colour of activity, orange is often used as the colour of