Ricoh AP204 Operator's Manual page 9

Printed Color
Your printer produces full-color output using four toner colors: cyan, magenta,
yellow, and black. These four colors make up the CMYK color model.
Note
Mixing CMY in equal proportions should hypothetically produce pure black,
but imperfections in the ink cause an equal measure of these colors to produce
a muddy or dark brown. Black toner is added to the color model in order to
make it possible to produce pure black.
If an image consisted of nothing by cyan, for example, cyan toner would be used
by itself and there would be no problem producing the desired color. Full-color
printing, on the other hand, required reproduction of tens of thousands of subtle
colors. These can be produced by controlling the relative proportions of the CMYK
toner particles printed within a unit area.
Relatively dense and light shades of the same color also can be reproduced by
controlling the volume of toner in a unit area.
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