Teribus "The subtractive system governs the fields of printing, painting, etc, where the perception of colour comes from an external light source striking the surface of the object. The three primary colours are Red, Yellow and Blue. Mix those and you get Black

The three subtractive primaries are Magenta, Cyan, & Yellow. Mixed in various combinations, these give "full colour" printing.
Mixed in equal quantities these pigments theoretically should give black. Since no pigment is perfect, this "black" tends to be visibly less than perfect. Therefore, most full colour printing systems use at least four pigments. Magenta, Cyan, Yellow, and Black.

This looks like I'm trying to be a smartass, but that wasn't the intention. I just deal with these colours a lot.
For those who don't, Cyan is similar to turquoise, while Magenta is a sort of pinkish-purple.