Black is not considered a color, as it is the absence of color. In physics, color is based on wavelengths, and with black there is no wavelength. In the visible spectrum of light, black absorbs light, creating an absence of color.
Black is the impression that human eyes receive when no visible light reaches them. Black pigment or dyes are composed of several pigments that collectively absorb all the colors, resulting in black due to the absence of all other colors. Black surfaces are able to act as thermal collectors because they absorb light and, as a result, generate heat.