Color influences us in many ways. It affects our thought process, guides our emotional response, and can even provoke a physical reaction. We use color-based phrases to describe emotion (seeing red, feeling blue or being green with envy) or attribute characteristics (cowardly yellow, black hearted, red blooded). Lack of color is associated with deprivation, while vibrant color connotes richness and vitality.
Color results from energy waves grouped in a color spectrum, and the visible spectrum is the part of the total spectrum that can be seen by the human eye. In Opticks, Sir Isaac Newton provided an early explanation of the visible spectrum and organized a color wheel or color circle to show the relationship between the colors in the visible spectrum (violet, blue, green, yellow, orange, red). A rainbow is a familiar representation of the visible spectrum.