A green screen stands for a blank background that can become anything. Dream books read it as possibility, and as the sense that the setting of your life is not quite real.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.