The color wheel diagram is a visual representation of colors arranged according to their chromatic relationships. It is used in various fields such as art, design, and color theory. The primary colors on the wheel are red, blue, and yellow, while secondary colors are orange, green, and purple. Tertiary colors are formed by mixing primary and secondary colors. The color wheel also includes concepts like complementary colors (colors opposite each other on the wheel), triadic colors (three colors evenly spaced on the wheel), and tetradic colors (four colors arranged in pairs of complementary colors).