Now, you can use other fractals of course, as the Graeiny was added in 7.5 Infinite I believe, it's just rather nice for this :)

By using metablobs or double sided terrains, you can create quite nice structures, and they can be multi-coloured.

Here is how I made the "Phlogiston" for Spelljammer, a fantasy space setting, where a rainbow coloured, gas-like material lies between Solar Systems.