Why does mixing colours on a screen make them brighter, while mixing paints makes them darker? Because there are two fundamentally different principles of colour mixing: additive light mixing (RGB, screens, projectors) and subtractive colour mixing (CMY, printing inks, watercolour, and gouache). The colour mixing simulator makes both principles interactively tangible and lays the groundwork for understanding photography, print, and design.
Step by Step: How to Use the Colour Mixing Simulator
- Select the mixing principle: Additive (RGB) for light sources, screens, and digital display; subtractive (CMY) for printing inks, watercolour, and gouache.
- Adjust the primary colours: For RGB, three sliders for red, green, and blue (each 0–255). For CMY, three sliders for cyan, magenta, and yellow (each 0–100%).
- Observe the mixed colour: The simulator shows the resulting colour in real time. RGB: all three at maximum = white. CMY: all three at maximum = theoretically black (in practice a dark greyish brown).
- Explore complementary colours: In RGB the complement of red = cyan (0/255/255); in CMY the complement of cyan = red. Complementary colours cancel each other out in the mixing process.
- Apply the insights in practice: Colour temperature corrections in Lightroom are based on RGB complement logic; colour corrections in print prepress work with CMY opposites.
Practical Examples
Example 1 – Additive (light): A smartphone LED torch (white) = full RGB mix. Stage lighting: a red spotlight + a green spotlight on the same white surface produces yellow light (R 255/G 255/B 0). Three primary-colour spotlights on the same point = white light.
Example 2 – Subtractive (print): Yellow printing ink absorbs blue and reflects red and green. Cyan printing ink absorbs red and reflects green and blue. Yellow + cyan mixed = reflects only green → green printing ink.
Example 3 – Black in four-colour printing: Although CMY theoretically produces black, four-colour printing (CMYK) includes a separate black channel (K = Key). Reason: CMY mixed black is greyish-brown and uses a large amount of ink. Pure K is deep black and more economical.
Understanding Additive and Subtractive Colour Mixing
Additive (RGB, light): Red + Green = Yellow; Red + Blue = Magenta; Green + Blue = Cyan; all three = White. Subtractive (CMY, print): Cyan + Magenta = Blue; Cyan + Yellow = Green; Magenta + Yellow = Red; all three = Black (in theory).
Frequently Asked Questions (FAQ)
Why is there a separate black channel in printing (CMYK instead of CMY)?
CMY mixed black is never truly black in practice — it is a dark greyish brown. In addition, solid CMY coverage (100/100/100) would saturate the paper with a very large amount of ink (over-inking → drying problems, show-through). The K channel solves both problems at once.
Why does colour mix differently when painting compared to on a screen?
Paints work subtractively: each colour absorbs part of the incoming light. More paint = more absorption = darker. Screens emit light additively: more colour = more emitted light = brighter. These are physically entirely different processes.
What are complementary colours and what are they used for?
Complementary colours sit opposite each other on the colour wheel. Additive: red and cyan; green and magenta; blue and yellow. An orange skin tone in a photo is neutralised by a blue-cyan cast — colourists in video production use this deliberately for stylistic effects (the orange-teal look).
