What should be done to make violet cooler while retaining its hue identity?

Correct answer: Increase blue slightly

The governing concept is colour temperature within hue control. Violet already contains blue and red; adding a small amount of blue shifts its appearance toward the cool, bluish side while preserving violet as the dominant hue. Option A is correct because the adjustment is gradual. Large amounts of yellow, green, or orange introduce competing or complementary influences and can dull, neutralise, or change the hue identity.