Tank Exteriors are any sort of outer insignia or camouflage that a player applies to the outside of a tank via the Exterior menu. They come in 3 types: Camouflage, Emblem, and Insignia.
Camouflage comes in several types and is designed to conceal your vehicle when stationary--except in the case of Light Tanks, whose camouflage value does not change whether they are mobile or not. This is a very useful feature that makes Camouflage a great choice for any Light Tank.
Camouflage can be paid for with either Gold or Credits, for different lengths of time: 7 days, 30 days, and permanent.