Being the default paint, the color green is pretty common in Tanki X. Not to mention, as most players would rather spend their hard-earned diamonds on new turrets, hulls or even on upgrades, paints don't usually get changed that often, resulting in its use even among some of the more experienced players - and not only among newbies - in the game.
Similar to the default hull, the Hunter, the color green is not a color to underestimate. It is perhaps one of the more suitable paints to use to somewhat camouflage your tank on grassy maps like Massacre, so you could shoot at enemy tanks in a relatively safe position... until you get spotted that is.
However, its usefulness can be pretty much outshone by other "greenish" paints like Forester, Guerrilla or even Savanna - paints that you'll eventually have enough diamonds to buy. In spite of this, and especially considering that Green is a free paint, it is still a very good paint to start off with.