Hue
Hue is the part of a colour you can name: red, blue, green. It is the property everyone reaches for first and the one that carries the least structural weight in a picture — a fact every painter learns late and every designer learns twice.
Where the word comes from
Old English hīw meant form or appearance in general, not colour specifically. Hue only became a technical term once colour was separated into measurable dimensions — Newton spreading white light into a spectrum with a prism in 1666, and, much later, Albert Munsell in 1905 splitting colour into hue, value and chroma so that it could be taught in schools and ordered by number. Before that separation, a painter had no reason to speak of hue apart from the stuff that produced it.
In the studio
Which is the point: the old workshops did not think in hues, they thought in materials. "Blue" was not a position on a wheel but a purchasing decision between ultramarine, azurite, smalt and indigo — four blues with four prices, four degrees of permanence and four different behaviours under oil. Azurite goes greenish and turns to malachite over time; smalt fades to a dirty grey as its potassium leaches out; indigo is a dye pressed into service. Choosing the hue was inseparable from choosing what would happen to the painting in two hundred years.
Why it matters
Because hue is the loudest property, it hides the one that actually builds an image. Convert a Rembrandt to greyscale and it still reads: the light still falls, the head still turns out of the dark. Convert most failed paintings and they collapse into mud. Value carries structure; hue carries mood and identification. The same hierarchy holds on a screen, which is why an interface that works in greyscale will work in colour, and one that only works in colour is being held together by hue alone.
Today
The word has had a second, commercial life. On a modern tube of paint, "hue" is a legal disclaimer: "cadmium yellow hue" means there is no cadmium in it. The pigment has been replaced by a cheaper or less toxic mixture chosen to look approximately like the original. It is an honest label doing quiet work — the colour is the same, the material is not, and the material is what determines how it will mix, cover and age.
Pigments used: Ultramarine · Azurite · Cadmium yellow
See also: Rembrandt van Rijn · Claude Monet