Steps to reproduce:
1. Open user attached project
2. Select the ConcreteFloors0054_15_H_A texture in the project view
3. Notice that RGB colorspace is black in alpha channel areas
4. Change the texture compression quality to "Fast" or go to Project Settings -> Editor and change the Best ETC Texture Compressor from Etc2Comp Best to ETCPACK Best, then reimport the texture
5. Notice that the texture is displayed properly now

Expected result: Etc2Comp should not draw RGB colorspace black in alpha channel areas

Reproduced in: 2018.3.0a2, 2018.2.0b8, 2018.1.5f1, 2017.4.5f1, 2017.3.2f1, 2017.2.3p1

Did not reproduce on: Windows, iOS

Fixed in: 2018.2.4f1, 2018.3.0a5