Here is one topic on it where a CC member describes how they did it. There are other discussion on it if you do a search=) HTH some, Jen
http://forum.cakecentral.com/cammo-cake-ftopicp-927461.html#927461
If you work with fondant, you could just cut the various colors out in different shapes, then take a rolling pin over them to get them to stick together, then put the whole thing over the cake, etc.
Just an idea.. 
There are a lot of ideas here.. http://www.cakecentral.com/modules.php?name=gallery&meta=search&type=full&search=camouflage
Hope this helps,
Holly
I load up bags with different colors of crusting bc and tip 3. Pipe random blobs - about 10 at a time - then go back with little pieces of Viva paper towel and smooth. Don't use big pieces of paper towel, or the color may transfer from blob to blob. Just keep going in that fashion until the whole thing is covered!
http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=90691
I did the fondant thing described by Holly above, and it worked out GREAT. And this was back before I knew anything about fondant, so it was made out of wilton (gag) - thank God for the ganache underneath! I imagine you could get much the same effect by using Viva or Melvira over blobs of crusting BC, though. Just free-form it. However it comes out, just tell 'em you meant to do that! 
Camouflage is one of the easiest cakes to make. I used a #12 tip and piped the various colors and then used a sponge paint roller and rolled over all the icing. The colors just seem to fall into place on their own by rolling the roller over them.
Here's mine although there is a bit too much green: http://www.cakecentral.com/modules.php?name=gallery&file=displayimage&pid=679133
(DianeLM ~ I love that helmet!!!)
The cake that I did was milder greens..with shades of more brown colours.
It was for my sons 12th birthday right after he joined the Army cadets here.
There was nothing fancy about it. I just used a star tip on a handful of different shades of pukey greenish/brown (I used cocoa to tinge some of the colours..tastes better than it looks!)
I like the idea's I read above. I have yet to find Viva papertowels here in Eastern Ontario though. (believe me, I've looked in every grocery store & WalMart)
I did this for my nephew who is an avid hunter. I first stamped my crumb coat with leaf cookie cutters, outlined them in black so the camo pattern matched my nephew's sweatshirt in the photo. Then just piped random star in groups. It was soooooo simple.
Quote by @%username% on %date%
%body%