I'm assuming you know how to use the tile window in either StarForge or SCM Draft
If you want to use the black tiles in your map try to avoid using the default one (0-0) (it's the one you can choose in StarForge from the terrain box). When viewing those black areas of the map with Xtra or SCE they will not be drawn properly and it can be confusing (I'm sure some of you hate that). Other black tiles will not do that (I'm not sure about all of them, but every other one I tried doesn't).
Other Features:
If you want your black tiles to not have any creep from Zerg Buildings then pick black tiles from the same row as terrain which normally doesn't allow creep (like the rock ground in the bad lands, or water).
Other black tiles which allow creep/buildings will also allow you to build over top of them as long as the unit can reach the point where it starts to build. Triggers can also create buildings on some black tiles but won't make men, strange huh.
The black tiles from the creep row will allow units to unload on it, be created by triggers, hover to it (like scv when done building) but does not allow buildings (other than Hatchery). Those tiles are also one way for ground units, what I mean is once you get a unit on real terrain it doesn't want to go back.
(Could be a nice thing for an RPG, it would require no triggers).
Black tiles do inherit many of the characteristics from the terrain they are on the same row in like is creep allowed, terrain height (affects vision), but there can be odd differences and I can't guarantee they will always relate like that.
If you need a black tile to do something specific start by looking at a terrain type you know will have similar properties and test a black tile from that row. As far as I know all the black tiles in a row are the same kind.
I started messing around because I didn't want creep under the terrainless Zerg buildings for my map but I hope this info helps someone else too

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If this is a rewrite and the findings are already documented... doh, I'm sorry.
Edit:
If you want to test these out the best way would probably be to create a 4x3 spot using the black tile you are testing, make one square bellow that blotch with the type of terrain whos row the black tile is on (so you don't forget which one you used) and then try unloading units, building, and creating units or buildings with triggers on that spot.
If enough are interested I'll make a list of the most useful black tiles in each terrain setting.
I wish StarForge would reveal this type of information on the selected tiles.