I know that in most modern armies occasionally leaves and camo nets are used to camouflage vehicles and helmets of soldiers, unfortunately this hasn't been implemented in the ArmA series yet which led to "unlogical" disadvantages for vehicles and infantry without ghillie-suits.

I can tell from my own experience that the lack of this possibility sometimes led to vehicles and soldiers being spotted and often taken out from a distance while defending or moving through forests and areas with high amounts of vegetation simply because they had no chance of concealing themselves adequatly in game while technically in real life this possibility would have been at their disposal.

My suggestion is: add camo nets to the game which can be "attached" to vehicles and add the possibility to add leaves to headgear such as helmets and hats.

This video shows a practice of a german tank bataillon where you can clearly see leaves and camo nets on Leopard 2 and Marder Tanks, the video was recorded by a soldier of the german army and uploaded on the german army's youtube channel, the speakers speaks German btw.
http://www.youtube.com/watch?feature=endscreen&v=FUr64N8v-80&NR=1#t=7m03s

P.S The user "AD2001" had the idea to make adding camo nets to rifles possible, this would have a great impact on realism simply because real life snipers for instance use this technique as well and it is extremely efficient.
I will post a link for a picture where you can see this technique used by a US-sniper.
the picture: http://kitup.military.com/2012/01/navy-seal-sniper.html