Filmmaking / Directing : A production question for those interested in costume design and make up by Douglas Eugene Mayfield

I'm working with a writer on a low budget horror comedy. I plan to make the movie around Halloween this year. In thinking about the production, I have the following problem. There are two groups of zombie characters in this story. The first are characters who are dressed as zombies but are people who are simply celebrating Halloween. (Call them 'fake zombies'. FZ.) The second are characters who are 'real' flesh eating zombies (RFEZ) who are invading earth and happily munching on human beings as they go. What I would like to do is figure out a way to make the groups instantly visually distinguishable for the audience. Certainly what actions these characters take on screen will help with that. But if possible, i'd like to find ways to use costume and make-up to visually differentiate FZ from RFEZ. I suppose that as an invading army, the RFEZ could have uniforms. But somehow that doesn't seem so effective. All thoughts and suggestions appreciated.