Step 1: Understanding colour attributes.
- Hue refers to the attribute of colour that defines its pure spectral colour (e.g., red, blue, green).
- Saturation measures the purity or intensity of a colour.
- Brightness describes the perception of luminance.
- Intensity refers to the amount of light emitted or reflected.
Step 2: Selecting the correct option.
Since hue represents the fundamental characteristic of colour, the correct answer is b. Hue.