No, the Green Hornet isn't part of Marvel or DC Comics. It has its unique comic book history and storyline that's distinct from both of those major comic publishers.
There are so many visual novels out there, and without more specific data, it's hard to say if 'green green visual novel' is popular. It might be that it has a dedicated following in certain regions or among certain demographics. For instance, if it was released in a country with a strong environmental movement, it might gain more popularity there as it could resonate with the people's values.
The Avengers originated in Marvel Comics. Marvel has developed a vast universe of characters and storylines, and the Avengers are a key part of it. Their adventures have been adapted into various forms of media, including movies and TV shows.
Captain Marvel is Carol Danvers. She gained her powers through an interaction with alien technology and has become a powerful hero in the Marvel universe.
A 'green green visual novel' could potentially be about environmental themes. It might tell a story where the characters are involved in activities like conservation, or it could be set in a utopian or dystopian world where the state of 'green' (as in nature) is a central aspect. For example, the story could revolve around a group of people trying to save a green area from being destroyed by a big corporation.