Intermediate Colors
Intermediate colors are the "third" category of color. They are made by mixing a primary and a secondary color together. As you look at a color wheel, intermediate colors are made by combining the primary and secondary color that are NEXT TO one another on the wheel. Colors that are next to one another are called analogous colors and are the most similar. By most similar, I mean for example, green is next to blue on the color wheel. Green has blue in it (blue + yellow = green).
Combining a primary and secondary color that is across from one another will not give you an intermediate color. These colors are the most different from one another and are called complementary colors. When two complementary colors are mixed together, the result is a gray/brown color as they cancel each other out.
Intermediate Color Wheel Showing the 6 intermediate colors

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Only the intermediate colors are shown in this example. |
| Illustration from: Art Fundamentals Theory and Practice, Ocvirk, Bone, Stinson, Wigg, 4th ed, 1981 |