Which mixture correctly forms a tertiary colour?

Correct answer: From a primary colour and an adjacent secondary colour

The defining rule is that, in the traditional colour-wheel system, a tertiary colour is made by mixing a primary colour with the secondary colour next to it. For example, red plus orange produces red-orange, and blue plus green produces blue-green. Opposite colours are complementary and usually create a duller neutral mixture; black and white create a value range, while equal amounts of all three primaries do not define a standard tertiary colour. Therefore, option B is correct.