color    Spectral  light  evokes  in  human eye sensation of a particular  color depending on the wavelength of light involved. They are grouped into seven primary colors listed in Table CI.

                           Table - CI, Wavelength ranges for different colors

Wavelength (nm) Color

780 - 605 red

605 - 590 orange

590 - 560 yellow

560 - 500 green

500 - 470 cyan

470 - 430 blue

430 - 380 violet

The  color  sensation  depends  on spectral composition of light incident  on  eye  and properties of vision. Because the eye has the  property  of integral sensitivity, same color sensation can be produced by mixing different spectral components.

The color sensation associated with a light stimulus can be specified  in  terms  of  three characteristics namely luminance (brightness), hue, and saturation.

The hue of the color is an attribute that distinguishes it as red, blue, green etc.

Saturation refers to the degree of purity, that is the degree to which  it  departs  from white  light. When hue is diluted with white  light  its  saturation reduces, and it produces a tint of the color.

New  color sensation can be produced by two processes. The first process, called additive, lights of different hue illuminate a  white screen resulting in new color sensation. The second is subtractive,  example  of which are the pigments that absorb all other colors except the one that they reflect.

An  additive mixture of three primary colors red, green and blue  produces various colors, according to the amounts in which the components enter into the mixture (see Table CII).

Table C II. Additive mixture of primary colors

Constituent Colors Mixture Color

red and green yellow

red and blue purple (magenta)

blue and green cyan

red green and blue white

This method of additive mixture is used in color television. In color photography subtractive method is used.