A colour with a green, blue or purple bias — associated with calm, shade and freshness.
In Colourwise's classification, a colour whose OKLCH hue falls roughly between 130° and 320°.
Warm/cool is a design convention, not a measured physical property of light temperature.
Teal and slate blue are cool colours.
Cool colours are commonly recommended for bright, south-facing rooms where extra warmth is less needed.
Colourwise labels a colour cool when its OKLCH hue lies between 130° and 320° and its HSV saturation is at least 8%. The arc is wider than the warm one because it takes in green, cyan, blue and violet. As with warmth there is no instrument for it: the label records a convention that designers and decorators share, and the angles were chosen to agree with how those colours are usually described.
| Colour | OKLCH hue | Colourwise undertone |
|---|---|---|
| Sage Green #9caf88 | 128.9° | Neutral band |
| Pistachio #93c572 | 133.9° | Cool |
| Teal #008080 | 194.8° | Cool |
| Mauve #e0b0ff | 311.6° | Cool |
| Purple #800080 | 328.4° | Neutral band |
Sage green sits at 128.9°, a fraction short of the cool arc, while Pistachio at 133.9° is inside it. At the far end Mauve (311.6°) is still cool and Purple (328.4°) is not, because a purple with that much red in it reads as neither. Yellow-greens and red-purples are where people disagree about temperature, and the classifier declines to call them.
How this was calculated: OKLCH hue angle of each catalogue HEX value, set against the 130° to 320° arc the classifier treats as cool.
A cool grey or blue is used in a room lit mainly by warm white lamps in the evening.
Light with little short-wavelength energy cannot show a blue fully, so the colour dulls towards grey after dark. Either accept two characters, day and night, or choose lamps with a higher colour temperature and good colour rendering.
A chart uses a cool-to-warm scale to show low and high values.
Readers take blue as low and red as high only where the data has that meaning, as temperature does. For profit and loss or approval ratings the same scale carries the wrong connotation, and a scale built on lightness is safer.