Glad I could help. It's in the game description but not the game itself (lack of time). The idea is to shoot the robots (press space) and pass (hold space) on the humans. The color system is an aid, but not a guarantee. Look for evidence of robot parts on the image window.
I set it up so:
1. Easy stage the color is always correct. This is to train the player to rely on the system.
2. Medium: the color is sometimes correct. Now the game is in full swing and you have to engage the mechanics fully.
I updated and bolded the instructions on the game page so it's easier to understand