Colour Theory
Colour Theory
This domain tests hue, value and chroma, colour mixing, and the effect of light on a match. Exam questions often ask why a colour matches in one light and not another.
The dimensions of colour
- Hue is the family name, such as red, yellow or blue.
- Value is lightness or darkness, from black to white.
- Chroma or saturation is the strength or purity of the colour.
- The Munsell system arranges colours by hue, value and chroma.
Mixing and relationships
- Additive mixing uses red, green and blue light; all three give white.
- Subtractive mixing uses cyan, magenta and yellow pigments; all three give near-black.
- Complementary colours sit opposite on the colour wheel and neutralise each other.
- Analogous colours are neighbours and harmonise.
- Metamerism occurs when two colours match under one light but not another because their pigments have different spectral curves.
- Simultaneous contrast makes a colour look different against different backgrounds.
Worked example
A repaired panel matches the original under daylight but looks greener under tungsten shop light. The pigments are metameric: the repair used a different combination with the same daylight match but a different spectral curve. The practical fix is to check the match under both daylight and tungsten, then adjust the pigment blend or use the original formulation.
Traps
- Adding black to darken a colour; it also dulls and shifts the hue. Use a complementary or a darker version of the hue.
- Judging a match under coloured shop lighting.
- Assuming a computer match is correct without a visual check.
- Forgetting that sheen and texture affect perceived colour.