To be green
Used to describe someone who is immature, or inexperienced
He can be rather green sometimes. I don’t think he’s ready to be promoted to a higher position yet.

Green with envy
Used to describe someone who is extremely jealous, full of envy
When we were children, my older brother always used to get green with envy if my dad bought something for me and not for him.

Give someone the green light / get the green light
When someone receives, or is given, permission to go ahead with something
We have been given the green the light by the Marketing Executive to go ahead with the new advertising campaign.

Grass is always greener on the other side
Used to describe a place that is far away, and better than, where you are now, or another person’s situation that is very different from your own
He realised that the grass is always greener on the other side when he saw that his new job wasn’t perfect, and had its own problems too.

Green belt
An area of fields and trees around a town
Our city has a policy of increasing the green belt around it.

Green thumb/green finger
Used to describe someone with a talent for gardening, having the ability to make plants grow
This garden used to look so beautiful when my mum lived here. She definitely had a green thumb. I wish I did too!