The etymology of the phrase 'salad days.'

"Disclaims Cleopatra: “My salad days, When I was green in judgment: cold in blood, To say as I said then!”

"In that earliest airing, “salad days” indicated a distant time of youthful naïveté. The descriptor “green in judgment” explains the curious phrase’s meaning: salads are green, and “green” is often used in the English language to denote someone who is inexperienced (e.g., greenhorn), hence the play on words. Salads are also cold, hence the further tying of “cold in blood” back to the phrase."

"Over time, the meaning of the phrase has moved away from being foolish because of a lack of experience and into a quick way of identifying a time in a person’s life when he was full of vim and vigor. The “foolish” component of “salad days” has dropped away, leaving only the “young” aspect in play. “Salad days” now also describes being at the peak of one’s abilities, which just goes to show how much a phrase’s meaning can change, if you wait long enough."