Painting your airsoft gun is a great way to add some personality to your weapon and to give it a unique look. It also is a great form of camouflage. Most guns come in black, which is not a very good color as far as camo goes. It sticks out, as nothing in nature is entirely black.
The best paint you can buy at your local hardware store is Krylon Fusion Camo. It comes in tan, brown, and green. It is flat matte and bonds to the material that you are painting pretty well. Generally I let the paint cure for about a week before touching the gun much.
When painting camo, it is best to start off by painting the whole gun in tan. Once that coat is dry(let sit for about an hour), you can add the green and brown. You can free hand or cut out stencils to apply the next two colors. An interesting technique I used on my BAR-10 was to put netting down when putting the brown on. As seen in this photo:
I did a brown base and free handed green on my G36c:
Hopefully these designs will inspire you to paint your own gun. It is fun, easy, and if you mess up, you can just paint over it, or sand off the paint. Good luck!