Hue, saturation and lightness

Hue

Hue is what most people mean by the word colour. It is the answer to the question of whether something is red, yellow, green or blue. Hues are usually set out in a circle and given as an angle, with red at 0 degrees, green at 120 and blue at 240. Black, white and grey have no hue and are called neutral or achromatic, which means without colour. Pink and maroon share the red hue. Sky blue and navy share the blue one. What separates them is the other two qualities.

Saturation and chroma

Saturation describes how far a colour stands from grey. A ripe tomato is highly saturated. A brick is a less saturated version of a similar hue. Take all the saturation away and only grey is left. You will also meet the word chroma, which means much the same thing in everyday use. Strictly, chroma is the absolute strength of a colour and saturation is its strength relative to its own brightness, but the difference matters mainly to colour scientists. Dull colours are not worse than bright ones. Most of what we see in nature and in a room is low in saturation.

Lightness and value

Lightness runs from black to white. Painters call it value, and many teachers hold that it matters most of the three. A picture with the right lights and darks still reads clearly in a black and white photograph, whatever its hues. Different hues reach full strength at different lightness. Pure yellow is naturally light and pure blue is naturally dark, so a dark yellow turns into olive or brown and stops looking yellow at all. Text is easy to read when its lightness differs sharply from its background, almost regardless of hue.

Colours on this page

Sources and further reading

• Hue on Wikipedia
• MDN Web Docs: hsl()
• Handprint: modern colour models
• Smithsonian Libraries: The Science of Color