CMYK

CMYK colours are a combination of CYAN, MAGENTA, YELLOW AND KEY(BLACK). In the printing press days when plates were being used the black plate was typically called the 'key' plate because it carried the most important key information relating to the artistic detail.

Computer screens display colours using RGB colour values.Printers often present colours using CMYK colour values.

In the print industry, cyan, magenta, yellow and black are used like paintings' primary colours. When you mix all the colours, you get grey. If you look at a printed page like a magazine with a magnifying glass you might see something like the illustration below.

All printed images are a mixture of these 4 colours, with different percentage out of 100. This could come in handy when trying to recreate the same colour by entering the same percentage as used before. The way in which photos are printed is by having an aluminium plate and letting the amount of percentage of ink of 4 colours onto the plate which transfer it to paper. Some examples of printing are offset lithography, flexography and so on.

So what would each colour look like if separated from each other in an image? Exactly like the image below.

You can see how different colours are made up of different strengths of CMYK. Because such printing uses inks of these four basic colours, it is often called four-colour-printing.

The RGB colours combined at 100-percent brilliance, produce white. The colours of CMY combined at maximum concentration, make black. Shades of gray result from the equal(but not maximum) brilliance of R,G, and B, of from equal(but not maximum) concentrations of C, M, and Y.

REFERENCE:

 http://www.webopedia.com/TERM/C/CMYK.html

http://cruxcreative.com/rgb-vs-cmyk-when-to-use-which-and-why/