Ask yourself two things before you start your design work:
1. What kind of story is this? Scary? Sad? Happy? About Halloween??
2. What color do you think of when you think about your story? If it is a happy story, do you think of yellow? If the story is set outside, do you think of grass (green) or the sky (blue)?
Finding a color that represents your story can be a good place to start your thinking.