CMYK and RGB are the two most popular color spaces.  CMYK color space is known as subtractive color & RGB is additive color.  CMYK stands for Cyan, Magenta, Yellow and Black and is used in print.  These four colors mix to produce a multitude of color within this color space.  RGB stands for Red, Green and Blue and is used in electronic displays like a television or computer monitor.  100% brightness of all RGB values creates a white pixel. Creating variations within the brightness of R,G or B produce a multitude of color within this color space.

RGB

CMYK