Green is the Colour
Green-Screening and Green-Lighting are always a source of confusion from the movie world. Both important and each very different.
Green screening is typically used during filming, when the actors need to be seen against a particular background. This could be in Superhero films with Spiderman swinging through the air above a panorama of New York, or simply to save the air-fare to film David Attenborough in London but against a jungle backdrop. The technique is to film the actors against a green background, carrying out whatever tasks are required. Then in the edit suite a piece of technological magic happens, and the green is removed from the screen and another background put in its place. This gives the impression that the actor is really in that modified environment. Sometimes an object is held by a person wearing a green suit (as can be seen on the picture) - when edited and the green removed this gives the impression that the object is floating in mid-air. Strangely, it is now unusual for a movie not to have some elements of Green-Screening.
Green-Lighting is a process where stakeholders in a proposed movie all get together to discuss the viability of the production. The actors may well run through some scripts, and even perform some songs if it is a musical. The stakeholders (director, producers, writers, etc) then decide whether to go ahead with shooting the film. Thus they give it the "Green Light".