Which adjustment shifts red-violet more toward violet?

Correct answer: Increase violet

The governing concept is proportional colour mixing: increasing one component shifts the mixture toward that component. Red-violet already lies between red and violet; adding more violet makes violet the stronger influence and moves the hue closer to violet. Increasing red would produce a redder result, while yellow or green would introduce unrelated colour influences and reduce the intended violet direction. Therefore, option A is correct.