Understand. Compare. Create.
Distinguish the primary colours of light, inks and paint to understand how they mix.
Primary colours are the starting colours of a particular mixing system. The useful question is therefore: are you combining light, printing with ink or working with paint? A colour can be primary in one model and secondary in another.
RGB is additive: the channels contribute light. Screens commonly use RGB colour spaces. In the sRGB examples below, each channel runs from 0 to 255. All three at zero give black; all three at maximum give white. This does not mean that sRGB can reproduce every visible colour.
CMY is an ideal subtractive model: colourants absorb parts of the light. Process printing commonly adds black, producing CMYK. Actual ink, paper and printing conditions matter; three theoretical primary names are not a reliable recipe for a particular printed result.
Red, yellow and blue are often used to introduce paint mixing. Treat this as a teaching framework, not a universal pigment specification. Two paints both called red can produce different mixtures. The pigments in your tubes, their proportions and the surface determine the practical range.
Background: Adobe on RGB and CMYK colour models.
At full channel intensity, combining pairs of RGB primaries gives cyan, magenta and yellow. Those secondary-colour names are the primaries in CMY: the model changes their role.
#00FFFF#FF00FF#FFFF00Each named channel below is at 255; any channel not listed is at zero. These are additive channel combinations, not equal-volume paint mixtures.
| Channels at full intensity | Result and HEX to copy |
|---|---|
| Red + green | Yellow#FFFF00RGB: 255, 255, 0 |
| Green + blue | Cyan#00FFFFRGB: 0, 255, 255 |
| Red + blue | Magenta#FF00FFRGB: 255, 0, 255 |
| Red + green + blue | White#FFFFFFRGB: 255, 255, 255 |
A 50/50 CSS color-mix() interpolates between colours in its chosen colour space; it does not switch both channels fully on. Do not use these rows as its expected results. The W3C RGB definitions explain the channel notation.
Keep the RGB or HEX value with each swatch. Try the RGB converter with red at 255, green at 255 and blue at zero, then lower just the green channel. The change is easier to understand when only one input moves.
Ask the printer for the required ICC profile and export settings before converting artwork. Compare a proof on the intended paper. A mathematical RGB-to-CMYK estimate cannot predict that whole workflow; the CMYK print guide explains the distinction.
Make small swatches using the paints you own. Label pigment names and proportions, let the samples dry, then compare them on the intended surface. Change one ingredient at a time. Keep a successful sample beside your notes instead of relying on its photograph.
The RGB table adds light; paint mixtures absorb light. Their result depends on the actual pigments and amounts. A screen demonstration cannot promise the same result from two similarly named paints.
In the RGB reference, they are the all-off and all-on channel combinations. In ordinary process printing, paper supplies the white while black has its own ink channel. Those roles differ from a painting lesson’s primary-colour list.
Get the free colour kit: HEX/RGB codes and a project worksheet.