I just thought I would throw this out here because Unity has this unusual quirk and it has driven me (along with some other very talented developer friends of mine) to the brink of cosmic insanity. If you have ever created a texture in Unity that has an alpha channel but the alpha information in Unity is completely incorrect, then it's most likely because you have "empty pixels" in your RGB channels.
How To Handle A Strange Unity Alpha Channel Problem
There is a maddening feature of Unity that will make you pull your hair out if you don't know what's going on. Here's what's going on.
Posted by Mantolith on - Basic Textures