Final answer:
In the Middle Ages and beyond, arsenic-based green dye was added to vegetables to make them appear greener and more appealing, albeit being notoriously poisonous.
Step-by-step explanation:
The question relates to historical food practices, specifically during the Middle Ages when people sought ways to make their vegetables appear greener and more appealing. To achieve this, dyes were added to vegetables. There is a notable practice of using arsenic-based green dye, which was notoriously poisonous. However, this practice was not confined to the Middle Ages and extended into later food processing periods as well. It is important to note that this practice was hazardous and that the dyes used were far from being safe or healthy.