What mainly happens when black is added to a cool colour?

Correct answer: The colour value becomes darker and a shade is formed

The governing concept is the difference between a shade and a tint. Adding black lowers a colour’s value, making it darker; the resulting darker version is called a shade. A cool hue such as blue or green normally remains cool unless its mixture is changed in another way. Adding white would create a lighter tint, while black does not change the colour’s complementary relationship or automatically make it warm.