Which colour pair will not produce a standard tertiary colour?

Correct answer: Red and green

On a conventional twelve-part colour wheel, a standard tertiary colour is made by mixing a primary colour with the neighbouring secondary colour, such as yellow-green, blue-violet, or red-orange. Red and green are not adjacent; they are complementary opposites. Their mixture tends toward a dull or neutralised colour rather than a named standard tertiary hue. Therefore, option D is correct.