They don't until your right on top of them.
And even then if they hide in trees it can be very difficult to find a single GV.
You think its bad now? GV's used to stick out like a black dung beetle on white carpet. Icons were visible at 5k plus. And you could see their dot farther out than that.
I do think camoflauge could be taken one step farther.
If the tank is stopped, engine off, should have the ability to hide your icon completely to simulate crewmembers jumping out & piling local vegitation or netting on the tank.
Want to put a time limit on it, fine. Say it takes 1 minute after a tank stops to be camoflauged. Soon as the engine starts, its gone, he has an icon again.
But give GV's the chance to "dig in" so to speak.