What should be done to account for some acrylic colours appearing darker after drying?

Correct answer: Dry a small sample to check the final value

The governing concept is the wet-to-dry value shift that can occur in acrylic films. Because the binder and water change as the paint dries, a colour may look somewhat different from its wet appearance. Option D is correct: test a small sample, let it dry, and judge the final value before applying a large area. Adding excessive white, using sunlight or judging only wet paint is unreliable.