Color modes differ for print and on-screen type mediums. The ways in which the colors are mixed are very different; therefore, they produce distinctly different choices.
RGB stands for red, green, blue color channels that are used by screens to build a light-based color system.Red | Green | Blue
RGB color mode in Illustrator.
CMYK stands for cyan, magenta, yellow, and black color inks that when mixed in various ratios create a wide variety of colors. This is often referred to as process color.Cyan | Magenta | Yellow | Black
CMYK mode in Illustrator.