An artist wants to cool yellow-green while keeping its value similar. What is the best method?

Correct answer: Add a little blue of similar value

The governing concepts are colour temperature and value. Blue is generally cooler than yellow-green, so a small amount of blue with a similar lightness can cool the hue while causing relatively little change in value. Thus, option A is best. Black lowers value, white raises value, and red introduces warmth and may also neutralise the green. The blue should be added gradually because a large quantity would overpower the yellow-green and create a different hue.