What is the best way to preserve local colour in shadow?

Correct answer: Add a controlled cool or complementary colour to the base hue

To preserve local colour, a shadow should remain related to the object’s base hue while becoming darker and often cooler or less saturated. B achieves this by shifting the original colour with a controlled cool or complementary mixture. Pure black can make the shadow dull and disconnected, while white or an unrelated bright colour destroys the object’s colour relationship rather than describing form.