If you buy new ink cartridges for your ink-jet printer, they come in the colors "cyan", "magenta" and "yellow". do you think that's weird? haven't we just learned that all colors are made of "red" "green" and blue", because that's what the color receptors in the human eye can see? why these complementary colors used?

Let's begin by explaining that a primary color is one that can not be obtained by mixing any other color.

In this sense, red, green and blue are the primary colors of light (using the additive theory of color), but not the primary colors of the pigments.

For the case of pigments (using the subtractive color theory) the primary colors are cyan, magenta and yellow. This is because the pigments generally absorb more light than they reflect (they absorb certain wavelengths and reflect others). Therefore, the color that a given object seems to have depends on which parts of the visible electromagnetic spectrum are reflected and which parts are absorbed.

Hence, according to the subtractive theory, if we join the three primary colors of the pigments, we will obtain the black. Unlike the additive theory of light, in which if we join the three primary colors we will get white light.