The creation of colors with red, green and blue works quite well with screens. But on paper this system can’t be used. On paper the subtractive color space CMY is needed. It uses the color components cyan (a kind of light-blue), magenta and yellow. Printing these colors reveals a problem: mixing the three components can‘t create a pure black. The result is more a dirty brown. As a result a fourth component was added: K, which stands for black.