CMY and CMYK Color Model
As the RGB color model is an additive color model, the CMY and the CMYK color model is based on the subtractive mixture of color. The characters stand for the components cyan (C), magenta (M), yellow (Y) and key (K, black). Cyan is a kind of blue, magenta is a kind of red, see color names for details. This color space is the basis for the modern process-color printing and therefore is used in the area of PC printers and the printing of colorful magazines or books, for example.
The individual components cyan, magenta, yellow and key are expressed in percentage values. 0% of one color means that the appropriate place is not stained by the appropriate color and 100% means that the appropriate place is stained completely with the appropriate color, while values between 0% and 100% means that the color is only applied in gradations. If a place is stained with 0% cyan, 0% magenta, 100% yellow and 0% key, it would result a pure yellow. If the place is stained with 100% cyan, 0% magenta, 100% yellow and 0% key, it would result in the color green according to the subtractive mixture of colors.
According to the theory, 100% cyan, 100% magenta and 100% yellow would result in a pure black. With today's printing colors it is not possible to realize this, so in the area of printing the additional component key (K, black) is necessary. Therefore, the difference between the CMY- and the CMYK color model is, that the CMY color model assumes that it is possible to mix black by all of the three pure colors and the CMYK color model uses black as an additional color. In the CMY color model, black is 100% cyan, 100% magenta and 100% yellow and in the CMYK color model, black is 0% cyan, 0% magenta, 0% yellow and 100% key. With the exception of pure colors, the CMYK color model also uses black for other colorful colors.
In the program pipette both the percentages for the CMY color space (fifth row: "CMY") and the percentages for the CMYK color space (sixth row: "CMYK") are provided. To appreciate both color models try to change some of the values of the CMY and the CMYK color model and look what is happening.