CMYK and RGB are two different colour models, and understanding the
difference can mean producing a great-looking insert rather than a
muddy, disappointing one. We’ll have to delve into a little science to
explain this difference.
The RGB colour model is used by monitors, televisions, scanners, and
digital cameras. A monitor uses very small bands of red, green, and
blue light to generate colour. RGB is additive because when you add all
three colours together, you get white light; when you turn off all
three lights, you get black. By mixing varying amounts of red, green,
and blue light, you can create most other colours.