The three variables that define what a color looks like are:

The answer includes brightness, hue, and saturation, which are indeed the fundamental attributes used to describe the appearance of a color.

Brightness refers to the perceived intensity of a color. It describes how light or dark a color appears based on the amount of light that it reflects or emits. Hue defines the attribute of color that enables us to classify it as red, blue, green, etc.; it refers to the wavelength of light. Saturation describes the purity or intensity of a color, indicating how vivid or subdued it appears. A highly saturated color looks bright and intense, while a less saturated color appears more muted or washed out.

Together, these three variables give a complete description of what a color looks like, enabling us to understand and manipulate colors effectively in various applications, such as graphic design, photography, and visual art.