The in-game gamma options should be much more limited than they are now. Even if someone decides to raise their monitor gamma, or apply a gamma effect through GPU software - it still won't have the effect it's having on the current version.
If you're truly concerned about PvP balance, there are much greater issues. Gamma is a second-class issue compared to:
-95% Damage reduction
-Double health, double stamina
-Instant Full-heal popping
-Guns have less range than paintball markers
-So many ways to cheese raid someone's base, that is, when the base protection features are even working properly
-Being able to glitch-view through objects
-Tons of dupe bugs in every single version, punishing the people who actually grind and play, the same people who will probably be "raided" while they were asleep or at work
-Still chinese and russians who join servers in creative mode and wreak havoc (Easy Anticheat, more like, lol-that-was-ez)
-Servers are still destabilized after ~24 players depending on hardware. Even the servers that shell on on crazy machines, and try hosting 40 players are experiencing many crashes, desyncs, and 3-4s lag on interactions.
I think we need to come to terms that this is just not going to be a PvP game. As someone who's only been PvPing since the start, I've found I've had to come to terms with this. The engine just doesn't do it well to begin with, and it's compounded by bad "balance" decisions that seem to be made based on the assumption that the player actually gets worse and becomes more stupid as they advance.