Only way to add texture that I know of is an object behind the territories. I added a star background to my succession wars map (it was just an image of space that I vectorized), but it made the file size way too big so I took it off. The only effects I added are the colored halos around the different 'Houses' and the logos for each as well:
http://warlight.net/SinglePlayer?PreviewMap=17952Like I said, the vectorized image worked, it was just too big (the map took a long time to load).
Edited 2/3/2014 20:51:59