I am using Unity 2018.3 and downloaded the new terrain tools as per the blog. In a new project, I imported a couple of texture packs and https://assetstore.unity.com/packages/3d/environments/landscapes/free-island-collection-104753 to use as a terrain base. Everything imported fine and I noticed that painting the terrain now uses terrain layers. My problem is that I cannot seem to paint over a layer with an existing (from _TerrainAutoUpgrade) or if I add a new layer. If I try to paint over one of the layers, it makes changes to a greyish shade instead of the new texture. Is it because of the terrain being imported with textures? If I create a brand new terrain it seems to be ok, except if trying to paint with the first texture over a subsequent colour. Then the same grey painting happens. Attached an image where I tried to paint black over exiting terrain layers to show what happens.