My bad, the directional light is also added to the shadowed part of the terrain, so the surrounding color need to be lighter than the shadow color in the ShadowBlack.png file to see a contrast.
For eg, this will work:
Result when directional light intensity = 0:
Result when directional light intensity = 0.5:
I think there’s a better way to achieve this and closer to what we would do with a real projector which would not use a spot:
This simply sets the spot intensity to 0 and modulates the base color with the projection texture color. For this to work as expected you should use the first picture, the one with a white filling color.