*Color*

The spectrum of color is a continuous one for which there has been several representation models [21]. One of the earliest models is called the Munsell color model, which organized the color perception into a color cylindrical space with three dimensions: hue, chroma (or saturation), and value (or lightness), as can be seen in Figure 10.

**Figure 10.** Munsell color system [22].

Hue refers to the color itself. Luminance means the brightness of a color. The higher the luminance, the closer it is to white, and the lower the luminance, the closer it is to black. Saturation is the vividness (clearness) of a color. As an example, 27 colors of varied hue, luminance, and saturation can be seen in Figure 11.

**Figure 11.** Colors of varied hue, luminance, and saturation [23].
