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

The idiom "red as a beetroot" is based on the visual resemblance between the deep red color of a ripe beetroot and the intense redness that can appear on a person's face. used to describe someone whose face has become highly flushed and red as a result of being exposed to heat or hot temperature. It emphasizes the intense redness of their complexion.