Anything used for print is CMYK; cyan, magenta, yellow and key (black). This colour process was purely a printing scheme which is why the colour yellow is used rather than that of green. If you were to print with RGB you would be unable to produce any yellow colours, the same as if you were to use RYB you could be unable to produce any green colours, which is why CMYK is used as it can create any colour. Most printers can’t interpret RGB, the colour process would fail and any print will be an off-brown colour which isn’t desirable. That being said, RGB is used for projection as screens can process the RGB colour scheme. If you were to go to a meeting, you would have to produce two copies; one in RGB and one that is CMYK.
The downside to CYMK colours is that they are never 100% correct. If you want any colour perfect, you will have to use a Pantone colour. However, these colours cannot be printed cheaply, they cost a lot of money as they have to be done professionally, they’re a specific mix of each colour. As well as this, when using colour within any Adobe software, you should use whole values, such as 25% rather than 24.9%, purely because this enables printing to pick up the colour easily and more accurately.