Color Modes Used in Printing
Red, Green, & Blue Light
The visible spectrum of light captured by cameras and displayed on TVs, phones, monitors, and tablets.
Cyan, Magenta, Yellow, & Black inks
Commonly called 4 color process or full-color printing. CMYK is never used for a light emanating display as it is pigment based. Only used for print.
Index color is RGB colors in an image that are limited to a palette of, at most, 256 colors in an entire image. PNG and GIF files use color indexing to make the image files smaller. Index color is only for web images.
Black & White or Grayscale
Grayscale images contain only black and white pixels. There is no HUE ( color ) or Saturation, just the Brightness or Darkness of the black to create steps, or scales ( percentages ) of the black.