Alpha Textures Removing Edge
Sometimes your alpha textures get this annoying edge around them. It sometimes looks like a shadow and sometimes looks like a white fluffy thing around the edge of your texture. This is due to the alpha channel not covering what it should, making it so that you end up seeing stuff you're not supposed to.
This is very annoying if you don't know how to fix it.
Fixes for it
Coloring Color Layers Under Alpha Layer
You can use Photoshop or Gimp to change the color of the pixels "under" the alpha. I'm not going to get into this because I haven't had much luck it this method.
Download VTBuilder, packaged with some other applications, from here: http://www.vterrain.org/Download/Binaries.html , get the simple install. Note: This is for Windows, you can find instructions for installing this on Unix systems (Linux, BSD, Irix, Mac OS X) here: http://www.vterrain.org/Distrib/unix.html
After installing Virtual Terrain Project, start up VTBuilder. Go to Project->Special->Process Billboard Texture in the menus. If you have a dark edge on your alpha texture enter 0 0 0 into the wizard pops up, if you have a white edge, enter 255 255 255. Now, click ok. A file chooser should pop up; select your alpha texture here (must be in png format). After clicking ok, it'll ask you for a output file, name this file something else so you don't overwrite your input texture. Set your age to use this texture and reexport. Your alpha edge should look very crisp and clean.
This is by far the easiest and most effective way of getting rid of this problem.