Three of my favorite things with green in the title:
The Green Man by Kingsley Amis. This a terrific ghost story. The twist is that the narrator is a black-out drunk and it's unclear whether he is actually seeing a ghost or just hallucinating.
Green for Danger. A great English detective story about a murder that takes place on the operating table.
A Flash of Green by John D. MacDonald. Maybe the best book written by one of the great writers of the last hundred years. This was also made into a movie with Ed Harris and Blair Brown but I haven't seen it in years.