I have been making maps a long time now, I have made a lot, and not encountered this problem before. Whenever I type the name of a custom Terrain Mask in, it comes up black. It's a png, I used the Red Green and Blue 0, 0, 255, and It's definitely RGB colour. I have tried switching rendering system, and re-saving the Mask with different names.
This map needs to be done soon... Thanks in advance for any help!