Against which type of background will yellow-orange appear warmest?

Correct answer: Muted blue-violet background

Yellow-orange is a warm hue, and its warmth becomes strongest when contrasted with a cool complementary or near-complementary background. Muted blue-violet supplies that cool contrast while remaining subdued enough not to compete with the subject, so option B is correct. A yellow, red-orange or cream background is warmer or similar in temperature and therefore reduces the perceived contrast and apparent warmth of yellow-orange.