This reminds me: can you make custom BLANKS for a specific terrain?
For example when you are fighting aboard a spaceship, you shouldn't see any scorched earth.
I figured it would be easier to just make a black starfield terrain and use it for outside. If you set the black tile to armor=255 and block walking, you can fly over it and you can't destroy it to reveal the scorched earth underneath.
edit: Here's a starfield MCD you can use. I might make a starfield map later.
edit edit: I improved on the starfield and made a mod to showcase it:
edit edit edit: STARS v. 0.2 has some minor alignment fixes plus more big stars and an alternate set of star background tiles which have fewer stars in them. STARS v. 0.2 is only the .mcd, not the showcase mod.