The base colour itself — red, blue, green, yellow and so on — independent of how light, dark or saturated it is.
The attribute of a colour corresponding to its position on the colour wheel, typically expressed as an angle (0–360°) in HSL, HSV or LCH colour spaces.
People often say 'colour' when they mean hue specifically — 'red' is a hue, but 'pale dusty red' describes hue plus tone and saturation.
Navy blue and sky blue have the same hue (blue) but very different lightness and saturation.
Hue is the first thing most colour relationships (complementary, analogous, triadic) are built from.
The CIE defines hue as the attribute by which an area looks similar to red, yellow, green or blue, or to a blend of two neighbours among them. In practice it is written as an angle around a neutral axis. In HSL and HSV the angle follows from which RGB channels are largest, with red at 0°, green at 120° and blue at 240°. In CIELAB it is the angle of the point (a*, b*), written hab, and in OKLCH it is the angle of the OKLab point (a, b). Munsell notation uses named steps instead of degrees: five principal hues and five intermediate ones.
| Colour | HSL hue | CIELAB hue | OKLCH hue |
|---|---|---|---|
| Red #ff0000 | 0° | 40° | 29° |
| Yellow #ffff00 | 60° | 103° | 110° |
| Blue #0000ff | 240° | 306° | 264° |
| Navy Blue #000080 | 240° | 306° | 264° |
| Sky Blue #87ceeb | 197° | 235° | 226° |
Blue and Navy blue share a hue angle in every column (240°, 306° and 264°), because navy is the same hue made darker. Sky blue sits 43° away on the HSL wheel at 197°, which is why Colourwise files it under cyan rather than blue. No two columns agree on any row: a hue angle is only meaningful with its colour space named.
How this was calculated: Hue angles from the catalogue HEX values through Colourwise's HSL, CIELAB (D65) and OKLCH converters, rounded to the nearest degree.
A design handoff gives a hue as a bare number and the developer types it into a different colour function.
The angle that means blue in OKLCH means violet in HSL, as the table shows, so the component ships in the wrong colour and nobody has made an arithmetic mistake.
A palette is generated by keeping the HSL hue fixed and changing lightness.
Blues drift towards purple as they lighten, because HSL hue is not perceived hue. Building the ramp in OKLCH, or correcting the pale steps by eye, avoids a scale whose ends look like two different colours.