What is the correct condition for forming a tertiary colour on the traditional colour wheel?

Correct answer: A mixture of a primary colour and its adjacent secondary colour

The governing colour-theory rule is that a tertiary colour is produced by mixing one primary colour with the adjacent secondary colour on the traditional colour wheel. For example, red mixed with orange gives red-orange. Option A is correct because the colours are neighbouring and retain a clear hue relationship. Opposite colours generally neutralise, black and white make a value change, and all three primaries do not define a tertiary hue.