What is the origin of the idiom "black and blue" and when to use it?

The idiom "black and blue" originates from the visual appearance of bruises, which often exhibit shades of dark blue and black. It has been used figuratively to describe the physical condition of having bruises since the 14th century. It is used to describe the discoloration and soreness that result from physical injuries, particularly bruises. It signifies that a person has been physically struck or injured, often resulting in visible marks on the body.