Painting Camo the easy way! :
Sure, you can paint camo by hand if you really want, but I'll demonstrate an easier way to do the job with an air brush and blu-tak (that stuff people commonly use for sticking posters to the wall).
I'll demonstrate on the left shouder of the Zaku II that I've primed already :
First, air brush on the main colour (that is the colour that will be seen the most), in this case I have used the Olive Green Tamiya Acrylic paint :
Once that has dried completely, apply the blu-tak to the piece, shaping it as you go to give it a few curved areas. If you are going to paint in more than two colours, I would suggest that you make the areas to be painted again, a little larger. This gives you room to add more blu-tak and apply another layer.
Now, air brush the second colour on, in this case I have used Brown Tamiya Acrylic paint.
Let that dry. Now, if you wish to apply a third colour, simply cover over some of the new layer of paint with some more blu-tak and air brush the third colour on.
Once the paint is completely dry, removed the blu-tak carefully otherwise you can chip and mark the paint. For the hard to remove pieces, simply push another piece of blu-tak against it and pull it off again. You might need to do it a few times but the hard to get off pieces will stick to it and come off.
If you wish to add more colours, then just repeat the process again but put the Blu-Tak in different parts, overlapping the last colour in places.
Now just lightly blacken around the edges using a fine brush and thinned black paint and your done!