In which situation can a dark complementary mixture be better than black for shadows?

Correct answer: When colour richness must be retained with depth

The governing concept is colour temperature and complementary mixing in shadows. Mixing a colour with a dark complement can lower its value while preserving a subtle chromatic relationship with the lit area. This often produces a more lively shadow than using black alone, which may flatten the colour. Option A describes the opposite aim, while C and D are unrelated studio actions, so B is correct.