Thermal View will give you a greyscale view in the HUD. You will see through trees and bushes. Maybe even through buildings? But you won't see the tank's color.
With this flag you will be able to locate a tanks position even when far away as it's heat is higher than the environment. Even cloaked tanks can be seen.
I think the balance is given partly through the inability to identify a tank's color.
A counterflag could be a "Blinding Light Flag" (please come up with a better name. I'm not native english). A tank carrying this flag will be so bright in the TV-Flag owner's HUD that he just sees a bright white when looking into that tank's direction.
Another counterflag could be an "Ice-flag" making a tank as cold as the environment, making it hard to impossible to be seen.
Now please start the discussion…
