What is CMYK?
CMYK colors are the colors that are used in print processes.
Cyan (a blue-green color tone), Magenta (A pink-reddish
color tone) and Yellow were originally meant to be able to cover all
colors, but it later appeared that this was not the case - an even mix of these
three colors were supposed to make black, but it turned out that they made
more of a muddled brown. Besides, trouble with the alignment of these colors
made this troublesome.
To alleviate this, the concept of adding black as a separate
color was introduced. This was the Key color, which is where the K
in CMYK comes from. There are several reasons why K is used instead of B (for black). For one thing, the B is already in use (in RGB), which can be confusing. Also, the key colour doesn't *have* to be black - it depends on the colour of paper that is being printed on. Black is most common, though.
Why do we need CMYK?
When we are talking about light, we can say that all colors
can be made from the colors red, blue and green (RGB). Black is an absence
of any of these colors. To get white, you must add an equal amount of all these
colors. . When you see blue on your monitor, it looks blue because it radiates
a large amount of light in the blue portion of the light spectrum, and much
less at other wavelengths. This is why light is an additive system.
When we do printing, however, it is just the other way around
- To get black, we must add all the colors (CMY) or the key (K). When you see
magenta on a piece of paper, it is not because the paper radiates magenta
- it absorbs everything but magenta. This is why pigment / print
is called a subtractive system.
In theory, the RGB and CMY systems are fully compatible, following
the following system:
Red + Green = Yellow
Red + Blue = Magenta
Green + Blue = Cyan
Cyan + Magenta = Blue
Cyan + Yellow = Green
Magenta + Yellow = Red
What can't CMYK do?
Unfortunately, CMYK can't reproduce all colors perfectly - the
problem especially arises with green colors. To solve this, a CcMmYK system
has been devised, but this does not solve all problems.
When doing print work, printing works usually use a combination
of the CMYK processes and the PMS (Pantone Matching System).
Further reading: CcMmYK RBG, color theory
Munsell system Pantone system