The CMYK color model (process color, four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and key (black). source
Complementary colors are pairs of colors which, when combined or mixed, cancel each other out (lose hue) by producing a grayscale color like white or black. When placed next to each other, they create the strongest contrast for those two colors. Complementary colors may also be called "opposite colors".
The phrase cool color is used to describe any color that is calm or soothing in nature. Cool colors are not overpowering and tend to recede in space. For this reason, cool colors typically make a space seem larger. Examples of cool colors include green, blue and violet (think calming blue waters). Some also use cool colors to describe more neutral white and greys. source