Two Ways to Make a Colour
Overlap two beams of light and the mixture is lighter than either beam. Mix two paints on a palette and the result is darker.
Additive mixing combines emitters:
- Light sources add their power together.
- Red, green, and blue light combine to make white.
- Newton showed that colour is already in the light.
- Hermann Grassmann formalised these rules in 1853.
Subtractive mixing combines filters:
- Pigments absorb specific wavelengths and reflect the rest.
- A mixture must pass both filters, multiplying their reflectances.
- The result reflects less light, making paint mixtures darker.
| System | What combines | Primaries | All three combined |
|---|---|---|---|
| Additive | Light beams | Red, green, blue | White |
| Subtractive | Colourant layers | Cyan, magenta, yellow | Near-black |
| Painters' | Paint tubes | Red, yellow, blue | Dark brown |
Red, yellow, and blue are simply a workshop convention from the 1720s. Cyan and magenta are the true subtractive primaries.
The Munsell System
Any colour answers three independent questions. Albert Munsell organised them in 1905:
| Property | Question | Scale |
|---|---|---|
| Hue | Which colour family? | 10 major hues arranged in 100 steps |
| Value | How light or dark? | 0 for black up to 10 for white |
| Chroma | How intense or pure? | 0 for neutral grey, extending past 20 |
These three dimensions are fully independent. You can adjust one while holding the other two constant.
Value is perceptually non-linear. A value of 5 looks halfway to white, but it reflects only a fifth of incident light. The human eye compresses luminance heavily.
Common pitfall: Confusing the three dimensions. People often say "brighter" when they mean higher value, higher chroma, or a shifted hue. Identify which property you need to change before mixing.