In grade school, you were probably taught about the color wheel and that red, yellow and blue were the colors that all the others were made from. When it comes to commercial printing inks, this is not actually true.

If you’ve ever had something printed commercially in color, you may have noticed the letters CMYK somewhere on the order. This refers to the names of the colors of printing inks: cyan, magenta, yellow and key or black. Why isn’t it blue, red, yellow and black?

Over time, printers determined that the combination of cyan, magenta, yellow and black looked best and created the truest colors on a white background, which is what most paper is. The colors are built up in layers, with each color of ink in its own cylinder. As each color is applied, the cylinder is wiped, often with a composite blade, to keep the design sharp. The paper is allowed to dry between colors so that the ink doesn’t run.

Why isn’t it B for black? Where does ‘key’ come from? There is some debate about this question, but one idea is that B could cause confusion with ‘blue,’ but printers use cyan, so this isn’t very likely. It could be because black is the key color in printing. It creates outlines and shading in designs, so the presence of black is a key element. Another suggestion is that back in the 19th century when commercial printing saw rapid developments, ink used to be added by turning keys.

No matter how the names came about, the combination of cyan, magenta, yellow and black can be used to create any colors you need for printing. Not only that, by measuring the colors precisely, they can be repeated exactly, which means that the first piece in the run will look exactly the same as the last.

The next time someone tells you that red, yellow and blue can be combined to create any other color, you will know that this isn’t the complete story. If you are printing, it’s cyan, magenta, yellow and black.