I read this article in the New York Times today about animals blending in to their surroundings in order to survive.
As an exercise:
1) Take a moment to read the article.
2) Set a timer for 10 minutes and spend the time writing a brief monologue for your main character describing how they blend into their surroundings. Maybe they describe being a gay soldier in a Don’t Ask Don’t Tell military, or a British soldier posing as a Nazi soldier.
You probably won’t ever use this monologue in your screenplay but I guarantee it will help you find layers to your story and your character you didn’t know existed.