What is the origin of the idiom "red as a beet" and when to use it?

The origin of the idiom "red as a beet" is not definitively known, but it likely comes from the observation of the physical reaction of a person's face turning red when experiencing embarrassment or shame. The comparison to a beet, a vegetable with a naturally reddish color, serves as a vivid and relatable metaphor to describe the flushed complexion that can occur in such situations. It can also be used to describe situations where someone is confronted with unexpected attention, criticism, or humiliation.