Final answer:
A circular scale of the colors of the spectrum, or color wheel, illustrates complementary colors opposite to each other, as well as primary, secondary, and tertiary colors, and their relationships.
Step-by-step explanation:
A circular scale of the colors of the spectrum, commonly referred to as a color wheel, shows how colors interact with each other and their relationships. The color wheel typically displays complementary colors opposite each other. These are colors that, when placed side by side, create a bold contrast and when mixed together produce white light. Examples include purple and yellow, green and red, as well as orange and blue. The wheel also includes primary colors (red, yellow, blue), secondary colors made by mixing two primary colors (orange, green, purple), and tertiary colors that result from mixing a primary color with an adjacent secondary color.