Which component should be increased to make red-violet appear cooler?

Correct answer: Violet

Colour temperature depends on the balance between warm and cool influences within a hue. Red-violet already contains red and violet; increasing the violet component strengthens its cooler, bluer character and makes the mixture appear less warm. Therefore option A is correct. Increasing red would make it warmer, while orange and yellow would also push the appearance toward warmth rather than coolness.