What colour is and how we see it
White light from the Sun is a mix of all colours. A surface absorbs some colours and reflects the rest; the reflected light enters our eye and the brain names it. A ripe tomato reflects mostly red light. Inside the eye, three kinds of cone cells react to red, green and blue light, and the brain mixes their signals.
Colour also depends on its surroundings: the same grey looks darker on white and lighter on black. That is why artists judge a colour next to its neighbours, not alone.
The colour wheel: primary, secondary and tertiary
The painter's colour wheel bends the rainbow into a circle of 12 colours.
- Primary (3): red, yellow, blue. They cannot be mixed from other paints.
- Secondary (3): red + yellow = orange; yellow + blue = green; blue + red = violet.
- Tertiary (6): a primary + the secondary next to it: red-orange, yellow-orange, yellow-green, blue-green, blue-violet, red-violet. The primary is named first.
Printers and screens use other primaries (see mixing below), but the idea is the same: a few starting colours make all the rest.
The three dimensions of colour: hue, value, saturation
- Hue: the colour family, its name on the wheel (blue, orange).
- Value (tone): how light or dark it is. Add white → a tint (pink is a tint of red). Add black → a shade (maroon). Add grey → a tone.
- Saturation (chroma, intensity): how pure and strong it is. A fully saturated colour is vivid; a low-saturation one is dull and greyish. Mixing a colour with a little of its complement makes a broken, softer tone.
Squint at a picture: you then see only values. A good picture usually has a clear range from light to dark, even if the hues are few.
Colour relationships and harmonies
- Complementary: opposite on the wheel (red–green, blue–orange, yellow–violet). Side by side they give the strongest contrast; mixed as paint they cancel to a brownish grey.
- Split-complementary: one colour plus the two neighbours of its complement — strong but gentler.
- Analogous: two to four neighbours (yellow, yellow-green, green). Calm and natural.
- Triadic: three colours evenly spaced (red, yellow, blue). Lively and balanced.
- Monochrome: one hue in many values. Bichromy and trichromy: a picture made with only two or three colours. A limited palette gives unity.
Seven colour contrasts (Itten)
The Swiss teacher Johannes Itten listed seven ways colours can contrast: hue (pure different colours), light–dark (value), warm–cool (temperature), complementary, simultaneous (a colour makes its neighbour look tinted towards its complement), saturation (bright vs dull) and extension (quantity: a small area of a strong colour balances a large area of a weak one). Look for them in famous paintings and use them in your own work.
Warm and cool, light and paint, local and expressive colour
Warm colours (red, orange, yellow) feel active and seem to come forward. Cool colours (blue, green, violet) feel calm and seem to move back.
Additive mixing (light, screens): red + green + blue light = white; red + green = yellow. Subtractive mixing (paint, ink, filters): each colour absorbs some light, so cyan + magenta + yellow give nearly black; printers add black ink (CMYK).
- Local colour: the real colour of an object in plain daylight (a green leaf).
- Apparent (tonal, ambient) colour: what we actually see under changing light — the same leaf looks yellow at sunset and blue-grey in shade. Impressionist painters in the 19th century painted this changing light outdoors.
- Expressive colour: colour chosen to show a feeling, not reality (a purple sky to show mystery). Moving from local colour to expressive colour is a step from naturalism towards abstraction.
- Aerial perspective: far hills look paler, bluer and less sharp because of the air in between, so painters use blue and blur to show distance.
In watercolour, you lighten a colour with water and the white paper shows through. In gouache, an opaque paint, you lighten it with white.
Colour meaning, psychology and culture
Colours affect mood: red can feel exciting or alarming, blue calm or sad, green fresh, yellow cheerful. Film-makers use this on purpose — a cold blue tint for a lonely scene, warm orange for a happy memory. Designers use it in signs, packaging and websites.
Meanings are cultural, not universal. Red means joy and good luck at weddings in India and China, but danger on a road sign. White is a wedding colour in many Western countries and a colour of mourning in parts of Asia. Saffron, green, indigo and turmeric yellow have long histories in South Asia, where the dyes once came from plants and minerals; traditional Chinese colour names often come from nature too, such as plants, stones and the sky.
When you design, ask: Who will see it? What feeling do I want? Is there enough contrast to read it easily, including for people with colour-vision deficiency? Do not rely on red vs green alone to show meaning.
Key formulas and definitions
- Primary (paint): red, yellow, blue
- Secondary = primary + primary (orange, green, violet)
- Tertiary = primary + neighbouring secondary
- Tint = colour + white; shade = colour + black; tone = colour + grey
- Complementary colours are 180° apart on the wheel; triadic colours are 120° apart
- Additive (light): R + G + B = white; Subtractive (ink): C + M + Y ≈ black
Worked examples
1. What is the complement of blue-green on a 12-part painter's wheel?
Go 6 steps (half the wheel) round. Blue-green → blue → blue-violet → violet → red-violet → red → red-orange. The complement is red-orange.
2. Plan a calm poster for a library using an analogous scheme.
Choose neighbours on the cool side: blue, blue-green and green. Use a light tint of blue for the background, a dark shade of blue for the text so it is easy to read, and green for small highlights.
3. A student paints a sunset and the far mountains look too close. How can colour fix it?
Use aerial perspective: make the far mountains paler (lighter value), cooler (bluer) and less saturated, with softer edges. Keep warm, strong colours for the front.
Common mistakes
- Mixing complementary paints to get a bright colour. They cancel each other and make a dull brown-grey.
- Thinking light and paint mix the same way. Red + green light makes yellow, but red + green paint makes brown.
- Mixing up value and saturation. Value is light vs dark; saturation is bright vs dull.
- Believing a colour means the same thing everywhere. Colour symbolism depends on culture and context.