As far as static grass goes, Gale Force 9 has an autumn/winter grass that doesn't clash so much with a brown base; the regular
GW "springtime" grass looks very bright.
Here's an Ork I did to show you what I'm talking about. I do basically what Vandez does, except instead of the bleached bone I used Earth brown (that's the Vallejo name, and I think the
GW name is very close). It has the bright green grass, which you can see in the background.