Which colour is commonly added to make another colour darker?

Correct answer: Black

The governing colour-mixing concept is a shade. Adding black usually lowers the lightness or value of another colour, creating a darker version known as a shade. Thus option A is correct. White does the opposite by producing a lighter tint, while yellow and pink may alter hue but are not the general material used to darken a colour in basic art instruction. The rule is: colour plus black equals shade; colour plus white equals tint.