Which colour is mixed with red to make red-orange?

Correct answer: Orange

The governing concept is the colour-wheel definition of a tertiary colour. Red-orange combines the primary colour red with the neighbouring secondary colour orange, so option B is correct. Red mixed with violet would move toward red-violet, and mixtures with blue or green would not have the red-orange relationship. In a compound colour name, both named colours usually indicate the colours that are blended to make it.