And now to paint your wagon. Well, island. We want it to be an isle of mystery and dooooooom. From the menu on the left, change from Heightmap to Textures mode. Select, say, Layer 5, then click the “...” next to Texture, choose Red Barrens from Tileset and RB_Red Mud from Texture. Then click over your island to paint it. Move the Intensity slider on the right to alter how saturated the color of the texture is - whack it up for a suitably alien reddishness.