CMYK is redundant.

If you consider yourself intelligent, and you consider yourself civilized, the rudiments of real numbers is not beyond you. If you are content with your mental block against mathematics, that is fine by me, so long as we don't need to work together.

We communicate colour data as three quantities between 0 and 1. The order differs according to the standard: sometimes (R,G,B), sometimes (B,G,R), or in other cases there may be additional factors.

Importantly, the value of Red is equal to the value of Cyan subtracted from 1: R = 1 - C; and similarly for the other primaries. In other words, if we have an RGB colour value of (1,0,0), we will print the CMY (0,1,1).

Now, it is a fact of printing that adding the three printing primaries does not produce a true black... black ink is required. But if we use the simple formula above, the RGB value of (0,0,0), which is a true black on screen, will be printed as (1,1,1).

It must be realized, however, that the simple formula given is a great oversimplification. Due to different printing processes, inks, and the varying luminance of emission primaries, (R,G,B) must be mapped to (C,M,Y) through a colour profile.

However, in my opinion, this could be done in conjunction with a colour optimizing routine, at the printing stage.

I believe it is merely for legacy reasons that we bring the black value (denoted K) into the colour data, which is then multiplied through the colour components for the purposes of screen display.

Note that K = 1 - Black: in other words, the amount of black ink is represented as (1 - K), so that it would be far more sensible, in my opinion, to call this amended colour space, RGBK.

A fortune-cookie for you: Tonight's the night: Sleep in a eucalyptus tree.