the subtractive color model most of us already know

When we learned to mix colors in grammer school, what we were learning to mix was subtractive color.

Three Primary Colors (Yellow, Red, Blue) are used to mix all of the other colors.

the way your printer produces
color with four inks

(the CMYK variant)

Cyan, Magenta,Yellow and Black inks are combined to produce all of the other colors. Although cyan, magenta and yellow should theoretically be able to make every other color, the reality is that the inks which are used don't have enough intensity to produce the depth of color needed for the deeper colors. Therefore, black (K) must be included.

For an explanation about the nature of subtractive color and how it differs from additive color (color mixed with colored light), please click here.