Light travels at 186,000 miles per second. It is the fastest of all the waves we can measure. Sound, by contrast, travels at 340.29 miles per second. For a long time humans believed that light traveled instantly. Einstein used it in his theory of relativity, which suggests that traveling at a speed greater than the speed of light would have an impact on time.
Light interacts with objects in a variety of ways. It is absorbed, reflected or refracted. If light strikes a black object, all the light waves will be absorbed, which is why black fabrics are so warm in the sun. Light is reflected off of glass or metal. Refraction is the change in direction of a light wave due to a change in its speed, which is caused by the bending of the wave by the object. A mirror is a combination of refraction off the silver surface and reflection of the glass. Scientists have developed reflective and refractive indexes, which assign values to common materials and objects. For example, the reflective index of wood is lower than the reflective index of glass.
To have color you must have light, an object and an observer. Humans see in red, blue and green, so when light strikes a red apple, the green and blue wavelengths are absorbed by the object and the red is reflected. Our eyes are all different, but we all observe the red reflected light and traces of green and blue waves that are not absorbed.
Our eyes are essentially red-green-blue---or RGB---color devices, just like a TV or computer display. Since we all see color differently, scientists needed a way to talk about color and designed a tool called the color gamut, or "shoe sole," a map of all the color waves that humans can see. They then described something called the standard observer, which is the portion of the gamut that most humans can see. The International Commission on Illumination created the first standard observer in 1931 and although the commission has refined the 1931 standard, as of May 2010 it was still used by color scientists.
Color models represent a refinement of color theory and the standard observer gamut. Since each RGB device is different, the RGB color model is device-dependent. The CMYK model---for cyan, magenta, yellow and black---is a subtractive color model used in printing and is also device-dependent. To help translate colors between these two models, scientists developed a device-independent color model. This breaks down color wavelengths by hue, saturation and value, or HSV. This was a commercial necessity to assure that retailers, such as L.L. Bean, match colors between fabric, computer and printed catalog.