What are brightness, hue, and colourfulness?

The perceptual attributes brightness, hue, and colourfulness are defined as follows:

Brightness: attribute of a visual sensation according to which an area appears to exhibit more or less light.

Hue: attribute of a visual sensation according to which an area appears to be similar to one, or proportions of two, of the perceived colours red, yellow, green, and blue.

Colourfulness: attribute of a visual sensation according to which an area appears to exhibit more or less of its hue.