Colour theory
Warm and cool colours
Reds, oranges and yellows are called warm, blues and greens cool. It is a convention about feeling, not about heat.
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Warm colours are the reds, oranges and yellows. Cool colours are the blues, blue-greens and blue-violets. The split comes from association: fire and sunlight on one side, water, shade and ice on the other. It is a useful shorthand in painting and design, but it is a convention, and the physics of light runs the opposite way.
Where the line falls
Most wheels are cut in two between yellow-green and green on one side and between red-violet and violet on the other. Green and purple sit near the border and can lean either way. Warmth is also relative. Painters talk about a warm blue, meaning one that leans towards violet, and a cool red, meaning one that leans towards blue, such as crimson, as against a warm, orange-leaning scarlet. What matters in practice is the comparison between neighbours: a grey looks warm beside a blue and cool beside an orange.
What the split does
Painters have long used the split to suggest depth. Distant hills look bluish because of the air in between, so cool, pale colours read as far away and warm, strong ones as near. Sunlit surfaces are often painted warm and their shadows cool. In rooms, people tend to describe warm schemes as cosy and cool ones as fresh or spacious. Experiments on whether wall colour changes how hot a person actually feels have given weak and mixed results. The effect is mostly one of mood and description, not of body temperature.
The physics runs backwards
A piece of metal glows red when hot, then orange, then white, then bluish white as it gets hotter still. So in physical terms blue light belongs to the hotter source. This is why a light bulb sold as warm white has a low colour temperature of about 2,700 kelvin and one sold as cool daylight has a high one of about 6,500. Nor is the association the same everywhere. It is strong in languages with European roots, and studies suggest that young children learn it gradually, which points to habit and experience as its source.
Colours on this page
Sources and further reading
Original text by the Rang desk, written with AI assistance and checked against the sources above. Meanings of colour vary from place to place and person to person. If we have something wrong, tell us.