If the amount of blue is gradually increased in yellow, in what direction will the colour shift?

Correct answer: From yellow-green toward blue-green

Yellow and blue are mixed to produce green. At the beginning, when yellow is dominant, the mixture appears yellow-green. As more blue is added, the balance moves through green toward blue-green. This is a change in colour bias caused by altering the proportion of the two pigments, not a change from orange, violet, or grey. Thus the progression described in option A is the most suitable answer.