What is generally produced by mixing black with an acrylic colour?

Correct answer: Darker shade

The governing colour-theory concept is a shade: adding black to a colour generally reduces its lightness and produces a darker version, so option D is correct. Black should be added gradually because a small amount can strongly change the mixture and excessive black may make the result dull. White produces a tint, not a shade, so option A is wrong. Mixing black does not automatically create white or a transparent layer, which rules out B and C.