International Standards and Conformity Assessment for all electrical, electronic and related technologies
Main title

Colour Management



RGB vs. CMYK, or additive vs. subtractive colour

Description of picture

RGB: the additive
colour model
Image courtesy of
Scall Olswald

Additive colour synthesis - RGB

Additive colour synthesis creates colour by mixing various proportions of two or three distinct stimulus colours of light. Adding all colours from a light source together makes white. Sunlight (white light) splits into different colours when it passes through a prism. When light is absent, darkness (black) is the result. Using this system, colour mixtures may not be what you would expect. For instance, adding green to red makes yellow. Examples of where you find additive colour are:

  • television and computer monitors
  • rainbows
  • light shows
  • fireworks
  • any light that comes directly to our eye from a light source


Description of picture

CMY: the subtractive
colour model
Image courtesy of
Scall Olswald

Subtractive colour synthesis - CMYK

Subtractive colour synthesis uses paints, dyes, inks, and natural colorants to create colour by absorbing some wavelengths of light and reflecting or transmitting others. With the subtractive colour process, white paper becomes darker as colours are mixed on it. Combining all colours in a palette on white paper will produce the colour black. Using this system, colour mixtures are what you would expect. For example, yellow and magenta make red. Examples of subtractive colour are:

  • computer printouts
  • photographic prints
  • most fine art excluding those pieces that contain light sources, such as neon sculpture
  • virtually any object that we see which doesn't produce light itself.