The opposite of "most white-hot" could be "coolest," "frozen," or "ice-cold." These antonyms indicate a lack of heat or a significant decrease in temperature. "Coolest" suggests a comfortable, refreshing temperature, while "frozen" and "ice-cold" convey a sense of extreme coldness. Other possible antonyms for "most white-hot" may include "warm," "tepid," or "lukewarm," which describe temperatures lower than "most white-hot" but still above freezing. Choosing the appropriate antonym depends on the context, as well as the writer's intention to convey a particular meaning or mood.