What should be added to make an overly green blue-green mixture more blue-green?

Correct answer: A little blue

Blue-green is made from blue and green, with the final appearance depending on their relative proportions. If the mixture looks too green, the governing principle is to add a small amount of the blue component. This shifts the hue toward blue while retaining some green. Yellow would push it toward yellow-green, red may dull it, and white only raises lightness. Therefore, option B is the suitable correction.