I've been just screwing around with photoshop a ton lately and I figure I would share with you all. Keywords will be in bold.
Start with a White document with desired size. Resolution does not matter for this tutorial.
Go to Filter --> Artistic --> Sponge and use the following parameters:
To give it a more cloth like look go to Filter --> Texture --> Texturizer and use the following parameters:
You are done with your camo look. If you would like to add color see below, if not, have fun your finished!
If you would like to add color, simply click Ctrl + U. Check "Colorize" and you can mess around with the parameters until you achieve the look you want.