Which of the following is not a secondary color?

• A. Green
• B. Orange
• C. Purple
• D. Blue

Answer: (D)

Secondary colors come from mixing two primary colors. In pigment-based color mixing used for PMU, the primary colors are red, blue, and yellow. Mixing these primaries yields green (blue plus yellow), orange (red plus yellow), and purple (red plus blue). Blue, however, is one of the primary colors itself and is not produced by combining two primaries, so it is not a secondary color. Therefore, blue is the color that is not a secondary color.