What happens when black is added to yellow-green?

Correct answer: A darker shade of yellow-green will be formed

The governing concept is colour value: adding black lowers the lightness of a colour and produces a shade. Therefore, black added to yellow-green creates a darker yellow-green shade while retaining the original colour family. White would create a lighter tint, and adding black cannot turn the colour into red or make it a primary colour. Hence, option A is correct. The useful rule is black produces shade, white produces tint, and grey produces tone.