Using colour: warm, cool and complementary colours

1Why this matters

Stand in a classroom with a metal roof on a hot afternoon in Bugesera, then in a stone house on a cold morning in Musanze. The right colours can make the first feel a little cooler and the second a little warmer, even though the temperature does not change. Colours can also calm people down, wake them up, make a notice easy to read from far away, or make a bright paint softer.

This lesson covers three principles decorators use every day: colour temperature, complementary colours, and how mixing a colour with its complement changes it.

2Warm and cool colours

Warm colours are the reds, oranges and yellows: the colours of fire and the sun. Cool colours are the greens, blues and violets: the colours of water, leaves and shade. This idea is called colour temperature, although the paint itself is not hotter or colder.

Temperature is also relative: every hue has warmer and cooler versions. A red that leans towards orange is a warm red; a red that leans towards violet is a cooler red. A blue that leans towards green is cooler than a blue that leans towards violet. When two versions of one colour clash, it is often because one is warm and the other is cool.

3Complementary colours

Complementary colours are pairs that sit opposite each other on the colour wheel. In the painter's system the pairs are red and green, yellow and violet, and blue and orange. Each pair contains one primary colour and the secondary made from the other two primaries, so together a pair contains all three primaries.

4Three effects of complementary colours

1. Side by side, they make each other look brighter. This strong contrast makes things stand out: a violet word on a yellow poster, an orange ball on a blue court.
2. Mixed together, they cancel each other out. Because a complementary pair holds all three primaries, mixing them dulls both. A touch of red makes a harsh green softer and more natural; equal amounts give a grey or brown. This is the painter's way to tone down a colour that is too bright, and a way to make browns for doors and furniture from colours already in the box.
3. They appear as after-images. If you stare at a colour for about 45 seconds and then look at a white wall, you briefly see a ghost of the shape in its complementary colour. This is why many hospitals dress surgeons in green or blue: during long operations the doctors stare at red blood, and green or blue clothing and cloths stop them seeing distracting green ghosts on white surfaces and reduce eye strain.

Worked example: the after-image experiment

1. Cut a square about 5 cm across from red paper, or paint one red, and stick it in the middle of a white sheet.
2. Put a small dot in the centre of the red square. Stare at the dot for about 45 seconds without moving your eyes.
3. Quickly look at a plain white wall or sheet of paper.

Result. For a few seconds you see a square of pale blue-green, close to red's complement.

Explanation. The parts of your eye that detect red become tired while you stare. When you look at white light, which contains all colours, the tired red receivers respond weakly, so for a moment you see white light with too little red in it, which looks blue-green.

Worked example: taming a bright paint

Mutesi bought a litre of bright lime-green paint for her bedroom, but on the wall the test patch looks harsh and tiring. What can she do without buying a new tin?

Step 1: find the complement. Green is opposite red, so red will dull it.

Step 2: add it very gradually. Pour a little of the green into a cup, add a drop of red, stir and paint a test patch. Repeat until the green looks softer, like leaves in the shade. Then mix the whole litre in the same proportion.

Step 3: check. Too much red turns the green grey-brown. If that happens, add more green.

She could also add white for a paler tint, but that would keep the colour bright. Adding the complement is the way to make it duller.

Practice

Solution. (a) Orange. (b) Yellow. (c) Red.

Solution. Cool colours, such as a pale blue or green. They make the room feel fresher and calmer, which helps pupils concentrate in the heat. Warm colours would make it feel even hotter.

Solution. Violet and yellow are complements, so side by side they give the strongest contrast. Violet and blue are neighbours on the wheel, so they look alike and the words blend into the background.

Solution. A pinkish red, close to magenta, because red lies opposite green.

Solution. Orange is red + yellow, so orange + blue contains all three primaries. Mixed together the three pigments absorb most of the light, so the colour cancels out towards grey or brown.