Having visible indicator lights on a helmet is a bad idea for a few reasons.
- Not very stealthy. If they're off for stealth why have them in the first place?
- Colors can be washed out/overpowered by other ambient light. If the light on your helmet is red because you're dying and you're in a room with red emergency lighting, or if you're in front of a very bright light source, it will be very difficult to determine your status based on this system. You'll have to use voice chat or some other form of communication that can be jammed/intercepted. Again, why use a visual system like this?
- The enemy can see them as well as you can. I don't think I need to explain why this isn't good.
Instead of using visual light, I would go infrared. It's not naturally visible, it is less susceptible to ambient interference, and there is a very large band of IR wavelengths that can be used. We already utilize infrared in certain military applications (IR tracer rounds that are only visible with the right equipment anyone?) and we can already filter different wavelengths of IR.
With the utilization of an IR passing filter that's built right into the helmet glass you don't have to worry about if you're receiving the right information. Let's say you're too close to an EMP and your systems go down, you can still see the messages from your squad without worry because you're not physically blinded.
However!
There are (imo) flaws with this system that greatly reduce its effectiveness. What about the guy on point? What about Bravo team that's in communication with Alpha? How do you solve the issue of requiring Line of Site? For this, we'll have to get creative. (I mean, it is the future after all. It's a shame that CIG hasn't gotten too crazy with the Sci-Fi side of things beyond FTL travel, laser guns, and aliens.)
To go beyond that, what would the system be used for? Simple communication? Health statuses? Ammo levels? If it's going to do a job that is already being done then it needs to improve on that system in some way. Also, you need to question if this is a job for the helmet, the armor, or a gadget. Many things can be integrated into a helmet without feeling like its there for the sake of being there, but you have to ask if a function is something that makes sense on a helmet in the first place. We're making something to sell here, not something that's "cool". Those aren't exclusive by any means, but if you're wearing a helmet it's because there is a chance of danger. At that moment, you want function first, form later.
I'm at work right now so I have to wrap this up, but let's hear some ideas.