The phrase "green as grass" refers to someone who is inexperienced or naive. However, there are a plethora of other ways to convey this same meaning using different synonyms. For example, you could say someone is "wet behind the ears," "fresh off the boat," or "a babe in the woods." Alternatively, you could describe someone as "unseasoned," "callow," or "untried." Each of these phrases offers a unique way to describe someone who may lack experience or knowledge. So, instead of relying on the same old tired phrase, explore other ways to express the same sentiment.