Thanks Michal
I can-t open your scene, because I use 3ds max 2018.... But I figured out, it has something to do with the material draget back to the material slot.
When I first did it, the top line in Geometry fp_grass must have bin selected, so therefore only some of the gras was addet the new color.
But still can't figure out, how to add the blevd correctly. If I select all in Geometry, and then drag the red line from the blend material to the material slot in Geometry, then all the grass is tinted..
And I can't drag if nothing is selected...!