As far as I can see there are a few things you can be doing wrong.. First of all, make sure your link to the texture looks like this: <Texture name="Border" file="Interface\AddOns\DBM-Core\textures\frameborder" level="TOP">
So make sure it has singel \ instead of \\ that most shared media links have now. And make sure the border file in the folder where it is linked to is named (in this case) frameborder.tga, but in the file leave out the .tga.
Second of all: The fact that it went from green to black can mean 2 things:
1) You fiddled with the color code?
2) You have a texture set for an icon instead of for a border? (So the file your loading to create a border is in fact a picture, and not a proper border texture?)