BUG DungeonEd (can't save Black Sky)

Hi people,
I have created my own dungeon. A crypt. So naturally i want the sky to be just black (it is underground), but no matter what I do, when I load my dungeon the sky changes to some of the coloured ones. Really annoying. Anyone has experienced this too, and know what I can do?
I have created my own dungeon. A crypt. So naturally i want the sky to be just black (it is underground), but no matter what I do, when I load my dungeon the sky changes to some of the coloured ones. Really annoying. Anyone has experienced this too, and know what I can do?