Why are red-orange and blue-green considered complementary on the colour wheel?

Correct answer: They lie opposite each other on a twelve-part colour wheel

The governing concept is complementary colour relationship. On a conventional twelve-part colour wheel, red-orange and blue-green occupy opposite positions, so they create strong visual contrast when placed side by side. Their opposition does not mean they are neighbours, made from the same base colour, or always equal in value. When mixed as pigments, they tend to reduce one another’s saturation and may produce a dull neutral.