This is related to this:
Basically the grass and the ground aren’t lit from the same angle, so the lighting wont match unless you alter the normals - even if the grass texture and ground texture are the same color of green.
Second, the grass needs to be the same green as the color of the lanscape material. If the lighting matches, but the color doesn’t, it’ll still look wrong.
Go into viewmodes and change it to “unlit” instead of “lit” to see just the base color of both, so you can tweak them to match without lighting to mislead you.
Once both the normals and the color are the same, you’ll get a nice looking natural blend.