Hey Junior,
When I use static grass, I use Verlindens which has a kind of a dark colour to it already.
Dont be affraid to use a brush when it comes to painting the static grass.
In stead of actually painting the grass, do whats called "dry-brushing"over all how leopold mentioned.
After you have dipped your brush into the paint that you want, wipe it off on a cloth(any size brush is fine w/ this method).
Once you have gotten the majority of the paint off, start applying the "dry-brush' method over the static grass. One thing to point out, dont do it w/ a heavy hand but go over the area(s) very lightly.
I have been using this type technique for some time w/ excellent results w/ out the aid of an airbrush
Dont get me wrong, you can use an airbrush but just think of the time in between cleaning it and the time of using a brush.
Awhile back I posted two picks of my Me262 and my Dewoitine D520 which I used this method on.
Flaps up, Mike
If you would listen to everybody about the inaccuracies, most of the kits on your shelf would not have been built Too Close For Guns, Switching To Finger