White light on its own, or white light shining through a blue gel, produces what are known as cool colors. Gels are thin sheets of colored polycarbonate (sometimes polyester) placed in front of the light to manipulate the wavelength, altering color. At a concert, cool colors would not be noticeable to an audience. They tend to be used in conjunction with warmer colors to give a more rounded feel to the performers on stage. Actors and musicians look a bit flat--they appear to lack depth--when only cool colors are used. Cool colors often are used to depict moonlight, or a scene taking place at night.
Yellow, orange and red lighting are known as warm colors. These are the main colors used at concerts and in theaters as they create an inviting ambiance, literally showing people in a good light. In the theater, warm colors commonly are mixed with a small amount of blue light to indicate daytime. Sunrise and sunset are created by increasing the ratio of warm lighting to cool lighting.
Cool lighting and warm lighting commonly are used together. A little blue or white light is useful for creating shadow and definition when predominantly warm lighting is being used. Even when showing a nighttime scene in the theater, most lighting directors use small amounts of orange or yellow to give a softer edge to the characters on stage.
Green is a color rarely used on its own, unless for a specific effect. It makes actors and musicians either look ill, or as if they have landed from another planet. Green is commonly used in conjunction with red and blue gels to create a range of other colors, such as yellow, cyan, magenta and pink. The latter two colors give a romantic feel to the stage, so are used in theater love scenes.