Why is caution needed when adding black to darken a colour?

Correct answer: Black can quickly dominate the original colour

The governing concept is making a shade by changing a colour’s value. Black pigment is visually strong, so even a small quantity can lower the value sharply and overpower the original hue. The result may become nearly black or muddy instead of a controlled darker version. It is therefore best to add black gradually and mix carefully. Black does mix with acrylic paint, does not automatically become transparent, and cannot dissolve a brush; option A is correct.