If a blue-green mixture is too blue what should be added to balance it?

Correct answer: A little green or yellow

The governing concept is controlled colour mixing: the dominant hue should be adjusted gradually with a compatible neighbouring colour. Adding a small amount of green or yellow shifts an overly blue mixture toward a more balanced blue-green. Red or violet would push the mixture toward other hue families, while black mainly lowers value and can make it dull. Therefore, option B is the most suitable correction.