The color wheel
Light uses color in an additive process to combine red, blue and green to make white. Pigment uses subtractive color to combine cyan, magenta and yellow to make black. I’ve had a few teachers and colleagues make a point to view images on a computer screen using CMYK, rather than RBG, because the images being worked on would eventually be printed out via CMYK printer.
The first image is rendered in CMYK, the second is RBG: