A red poster colour shadow looks heavy when made only with black. What is a more natural alternative?

Correct answer: Add a little green or dark violet to red

The governing concept is chromatic shadow mixing. Black can lower value abruptly and make a red shadow look flat, dirty, or visually heavy. A very small amount of a complementary colour such as green, or a related dark violet, can reduce the red’s intensity while preserving richer colour variation. Therefore option A is the best alternative. White creates a tint, yellow shifts the hue toward orange, and water changes dilution rather than producing a naturally coloured shadow.