Well, you can change the alpha by editing the second to last line. And, uhm, I'd change the color by editing the texture file, but I'm sure there's a way to do that in script, although how is entirely lost on me.
Ok, so I decided I wanted a nice, smooth round background for my minimap. I created the TGA, got it saved good, got it in game. One problem: it covers the map! Now, I could cut out just the right sized ring, but that would be... tricky. At least for me and my minimal photoshop skills. So I figured I could shove the texture to the back strata, right?