If yellow-green is the dominant colour in a scheme which tertiary colour will create the strongest contrast with it?

Correct answer: Red-violet

The governing concept is complementary contrast on the colour wheel. Yellow-green lies approximately opposite red-violet, so these two hues have strongly contrasting colour influences. Blue-green is nearby and therefore analogous rather than opposite; yellow-orange and red-orange are also on the warmer side and are not the complementary counterpart. Thus red-violet in option B provides the strongest contrast in this set.