The pictures don't do it justice I'm sure but here are a couple of tips.
The paint seems to have a gloss and reflects light. I would recommend using the flat camo paint in the cans at walmart. Stay away from Black as a color (does not occur naturally in nature).
You want to use a base color that blends in to your environment. I used a dark tan and did my whole rifle then went back over it with brown and flat green using natural vegetation to help break up the outline.
Think of the primary position your rifle will be in while you are shooting. I.E. Horizontal, in the standing, kneeling, or prone.
I typically shoot my DMR in the prone off of Bipods so I picked vegetation that grows around knee height to spray paint over and get the outlines and stuff.
The less man made that you can make the weapon look the better the camoflauge :
Remember typically the prettier the camo paint job the less effective it is