Painting depends on whether you want the appearance of green, growing grass or yellow, dead grass. For green grass, I airbrush the clumps of grass a dark forest or olive green, similar to the color of the border on this page. After this has dried, I would return to spray the middle to the tip portions a more yellow-green, leaving the base of the clumps in the darker green. Finally, I dry-brush the tips in light yellow for a highlight color. Dead grass is a similar procedure, but start with a yellow-brown color, working to a golden-yellow mid-tone and highlighting in light yellow to almost white. I always paint the grass on my dioramas first, then paint the bare ground, that way any green overspray is covered by the more brownish earth tones and allows for a smooth transition of color.