Which of the following combinations is not considered a tertiary color?

Tertiary colors are created by mixing a primary color with a secondary color, resulting in more complex hues. In the context of color theory, the primary colors are red, blue, and yellow, while the secondary colors are green (made by mixing blue and yellow), orange (made by mixing red and yellow), and purple (made by mixing red and blue).

The combinations such as red-orange, blue-green, and yellow-green fit the definition of tertiary colors. Red-orange is a mix of the primary red and the secondary orange. Blue-green is a combination of the primary blue and the secondary green, while yellow-green derives from yellow (primary) mixed with green (secondary).

On the other hand, blue-yellow does not represent a recognized color combination that results in a tertiary color. Instead, blue and yellow are primary colors and can create green when mixed, but they do not lead to a tertiary color as defined in color theory. Therefore, blue-yellow is the combination that does not align with the definition of a tertiary color.