This chapter reviews the fundamental concepts behind color and color theory, including the biological mechanisms behind the human color perception and the structure of different color models. Human eyes contain pigmented cells, called cone cells, that absorb visible light radiation and send signals to the brain in response. Individuals experience colors in different ways, resulting from their personal psychology and cultural experiences. Color hue is what most people think of when they hear the word “color” and includes all the colors of the visible spectrum. The brightness or lightness of color is commonly broadly referred to as value, particularly in computer applications. It is easy to conceptualize color value by imagining a color scheme in which both saturation and hue are held constant, such as a spectrum of grayscale that moves from white to gray to black. In some cases, cultural conventions guide readers to understand a palate of different hues as a clear sequential progression.