To test: get something with an enhanced rapid-fire X-ray laser to shoot at you when you're running level 8 or so armor (I used Tharsis plate). You'll get frequent red flashes, but you won't actually take much damage...generally only 3hp or so per hit.
I think the game may flash red based on projectile damage, rather than what is actually happening to the armor. It shouldbe based on actual damage to armor.
This isn't confirmed (since I don't have access to debug) and I'll readily close this if it turns out I'm misreading what's happening.