green as grass
(as) green as grass
1. Very green in color. The steady rocking of the boat caused Colleen to become green as grass.
2. Very inexperienced and perhaps naïve. This is a very important job, so I can't understand why they hired someone who's as green as grass.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
*green as grass
very green. (*Also: as ∼.) His face turned as green as grass just before he vomited.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
green as grassBRITISH
If someone is as green as grass, they have little experience or knowledge of something and trust what other people tell them too easily. I was a newcomer to the sport and as green as grass. Note: It is much more common just to say that someone is green. They admit they were very green when they arrived.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012