SPECTRUM
WHAT IS SPECTRUM
A spectral color is a color that is evoked by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths. Every wavelength of light is perceive as a spectral color, in a continuous spectrum. The color of sufficiently close wavelengths are indistinguishable.
The spectrum is often divided up into named colors, through any division is somewhat arbitrary and the spectrum is continuous. The traditional color include red, orange, yellow, green, blue, and violet.
HOW WE PERCEIVE COLOR
Technically speaking, color are the way our brain, by use of our eyes, interprets electromagnetic radiation of a wavelength within the visible spectrum. Visible light lies between 400 and 700 nano meters.
The difference wavelength are seen as different color, as in the spectrum below. You seea spectrum like this everything you see a rainbow.
Traditionally the spectrum is divided into seven separate band. The first person to really define this was Newton. Some people believe that he include the color indigo only to make seven steps to match the number of notes in major musical scale.