A form looks harsh because only black was mixed into its shadows. What is a better option?

Correct answer: Create a darker or cooler mixture of the local colour

The governing concept is colour-based shading: a shadow is usually a darker or altered version of the object’s local colour, not simply black added in equal quantity. For example, a blue form may use a deeper or slightly cooler blue in shadow, preserving colour relationships and natural variation. White removes the sense of shadow, leaving it blank breaks the form, and yellow is not suitable for every object. Therefore, option A is correct.