Hue
The attribute of a colour that gives it its name — red, green, blue — represented as a position on a circular scale.
Measured in
degrees (0-360)
In depth
Hue is independent of how light or how saturated a colour is, which is why it is separated out in HSL editing: shifting hue turns a yellow leaf orange without changing its brightness or intensity. Because the scale wraps around, adjustments near the red end can move in either direction to reach the same result.
Examples in practice
Rotating the hue of foliage by fifteen degrees converts a yellowish spring green into a cooler summer green.