Which colour can be mixed to make a darker value of another colour?

Correct answer: Black

The governing concept is colour value, which describes how light or dark a colour appears. Mixing a small amount of black with another colour generally lowers its value and produces a darker shade, so black is correct. White would raise the value and create a tint. Yellow or pink may alter the hue and brightness, but they are not the standard answer for making a colour darker. Black must be added sparingly because it can quickly overpower the original colour.