If yellow-green has the correct hue but is too bright, which colour should be added in a tiny amount?

Correct answer: Red-violet

The governing concept is complementary reduction of saturation. Red-violet lies opposite yellow-green on the colour wheel, so a tiny amount can mute excessive brightness while causing less unintended hue movement than a large correction. Yellow reinforces the existing direction, white increases lightness, and blue shifts the hue. Since the hue is already correct, option C best targets intensity alone.