Seeing as how the three primary colors are cyan, magenta and yellow (CMY), why do monitors and almost all the GUI components out there use red, green and blue (RGB)? (If I'm not mistaken, printers use the CMYK model.)
Is there a historical, hardware/software, or other reason for it?
The difference lies in whether mixing colours results in LIGHTER or DARKER colours. When mixing light, the result is a lighter colour, so mixing red light and blue light becomes a lighter pink. When mixing paint (or ink), red and blue become a darker purple. Mixing paint results in DARKER colours, whereas mixing light results in LIGHTER colours. Therefore for paint the primary colours are Red Yellow Blue (or Cyan Magenta Yellow) as you stated. Yet for light the primary colours are Red Green Blue. It is (virtually) impossible to mix Red Green Blue paint into Yellow paint, or mixing Red Yellow Blue light into Green light.
the 3 additive colors are in fact red, green, and blue. printers use cmyk (cyan, magenta, yellow, and black).
and as http://en.wikipedia.org/wiki/Additive_color explains: if you use RYB as your primary colors, how do you make green? since yellow is made from equal amounts of red and green.
This is nothing to do with hardware nor software. Simply that RGB are the 3 primary colours which can be combined in various ways to produce every other colour. It is more about the human convention/perception of colours which carried over.
You may find this article interesting.
The basic colours are RGB not RYB. Yes most of the softwares use the traditional RGB which can be used to mix together to form any other color i.e. RGB are the fundamental colours (as defined in Physics & Chemistry texts).
The printer user CMYK (cyan, magenta, yellow, and black) coloring as said by @jcomeau_ictx. You can view the following article to know about RGB vs CMYK: RGB Vs CMYK
A bit more information from the extract about them:
Red, Green, and Blue are "additive colors". If we combine red, green and blue light you will get white light. This is the principal behind the T.V. set in your living room and the monitor you are staring at now. Additive color, or RGB mode, is optimized for display on computer monitors and peripherals, most notably scanning devices.
Cyan, Magenta and Yellow are "subtractive colors". If we print cyan, magenta and yellow inks on white paper, they absorb the light shining on the page. Since our eyes receive no reflected light from the paper, we perceive black... in a perfect world! The printing world operates in subtractive color, or CMYK mode.
Source: Stackoverflow.com