I presume you mean in the CMYK colour model. There are two reasons, partly to avoid confusion with the B for blue, but mainly the K doesn't stand for "black", it stands for "key" - in printing the cyan, magenta and yellow had to be aligned (or keyed) with the black.
William K. Black was born on 1951-09-06.
Assume something (e.g. equations) using k then prove k+1 using k.
Tommy Lee Jones was refered to as K, or Agent K
Sharon K Black has written: 'Cable television for Europe' -- subject(s): Cable television
K. K. Usman has written: 'Exafs studies using synchrotron radiation'
bl-ah-k
calvin klein
36 Black Keys On a Piano36 B K on a P means 36 black keys on a piano.
Black
J. K. Jeglum has written: 'Strip clearcutting in black spruce' -- subject(s): Growth, Black spruce, Trees, Clearcutting
The letter K.
k