An artist wants to make violet relatively warmer. In which direction should it be shifted?

Correct answer: Toward red

The governing concept is hue bias within violet. Violet shifted toward red becomes red-violet, which is conventionally warmer than blue-violet because red contributes the warmer side of the colour relationship. Therefore option C is correct. Shifting toward blue increases the cool bias; moving toward green changes the hue away from violet, while adding grey mainly reduces saturation rather than making the colour warm.