3) What does “RGB” have to do with graphic files?

3) What does “RGB” have to do with graphic files?
RGB = Red-Green-Blue. Computer monitors use RGB to define the colours that appear on screen. Each color in the RGB combination is measured from 0 - 255. An example would be the colour blue, the RGB combination for this colour would be 0-0-255.
(Source: www.artisan-ds.com)