Red-violet has become too red. Which colour should be increased to shift it toward violet?

Correct answer: Blue

The governing concept is adjusting the ratio of component colours. Red-violet is produced from red and violet; in practical colour-wheel terms, increasing blue helps move a red-dominant mixture toward the violet side because violet contains red and blue. Green and yellow would introduce unrelated neighbouring hues. Although adding violet could also alter the mixture, increasing blue is the more direct component-based correction, so option A is correct.