The antonym of "most whitehot" could be "cool," "cold," or "chilled." These words all convey a sense of decreased temperature, and contrasting them with the intense heat of something described as "most whitehot" creates a clear shift in meaning. Another antonym could be "moderate" or "temperate," which denotes a lack of extreme heat or cold. In the context of emotions or reactions, "most whitehot" might have antonyms such as "calm," "composed," or "collected," all of which suggest a level-headedness or detachment that is absent from a state of extreme passion or anger.