Spectral Colors

A spectral color is composed of a single wavelength. For eg. spectral orange has a wavelength of around 600 nm. When we see the emission spectra of certain gases like hydrogen and neon they emit a characterstic spectra which is used in the identification of the gases. This is called electromagnetic spectroscopy.

So what colors are not spectral. Some common examples are white, black and gray. There is no wavelength of light that produces white color. Its just the cummulative result we see when equal amount of light of different wavelengths are reflected completely from a particular object. Black is when no color is reflected from an object. Gray represents the scenario when all the wavelenghts are equally absorebed/reflected by the object. Some other exams are pink, shades of violet, magenta.

Most of the color we see around us is non spectral in nature. Consider your CRT monitor. Its is composed of RGB phospors which combine to give you the 32bit colors. When orange is displayed on your monitor its in not the actual 600nm wavelength that is emitted by the phosphors. Its is a combination of 2parts of red and one part of green which gives you this color.

Why do we interpret both as the same color??
Becoz in the brain, the receptors do not respond to specific wavelengths. They respond to a variety of wavelengths. So lets say when the spectral orange hits the eye it illicits response in the red and the green cones. The response in the green cones is about half the response in the red cones. And the summation of the two responses help in identifying the color as orange. When the cones are stimulated using the mixed color from your CRT lets say a similar respose is generated in the brain again giving rise to the orange color.