The often-collaborator/sometimes-student/always-fun Pierre-Erick Lefebvre just asked me to look at his blog, and his new CMYK-controller + Psycho Chicken game. I can't wait to get my mits on it, but he says something in there about the K in CMYK being “Khol” (whatever), and that's where the evil-professor split personality kicks in and reminds anyone who will listen and everyone else what that damn K is for in the first place.
The Wikipedia CMYK entry wasn't so helpful about the origins of the K, but at least it got it right: K stands for “Key”. So I rooted around my study and found the following passage that works pretty good for me. It's from Getting it Right in Print, one of those how-to books that occasionally come in handy when working with the printer. From page 31:
*Most graphic designers know that the inks used in four-color process printing are cyan, magenta, yellow and black (CMYK). While it is reasonable to abbreviate cyan, magenta and yellow to C, M, and Y, how come black is given the letter K? Here is how I found out...*
*Towards the end of my very first day working in the printing industry, one of the printers told me that he needed a new “key plate” first thing the next morning. I had no idea what he meant and thought he was joking. When I eventually arrived an hour after him the following day, he was not happy, to say the least.*
*This was not good. When the presses stop, the shop is no longer printing money. A new key plate, I was rapidly informed, is a plate that prints the color that all the other colors key to: i.e. black. If you think about it, it is obvious. Text and image borders are typically printed in black. Printing them first often makes it easier to position — or “key” — the other colors to the job. So “key” is actually what the “K” stands for.*
*It is a common misconception that black is assigned the letter “K” because if it was called “B” it could be confused with blue. While plausible, this is not the case.*
So there, K stands for “key”. Now that that's out of the way, the pedantic academic can go back into hibernation.