rich black consists of 40 C, 40 M, 40 Y and 100 K (sometimes yellow is left out). Experienced operators adapt the mixture of colors to the content of the page. On pages that have a lot of cool colors like blue in them, they use a cool rich black which mainly adds cyan to the black. On pages containing a lot of warm brown colors, a warm rich black is used which contains more magenta and yellow than cyan.