I’ve spent a few days playing around with starfield concepts to establish a general mood. I originally wanted dark oppressive cloud-heavy backgrounds illuminated by electric storms, similar to these photographs I took last year:
However, It soon became apparent that I wouldn’t be able to recreate this exact look using the technology I’m working with (i.e., without a volumetric lighting model and some complicated pixel shaders) 
There might still be ways to fake it, however. We’ll see.
Instead, I’ve created a new system of generating starfields that consists of a static star background overlaid by various nebulae. The nebulae are random as well, but pre-baked into textures. I wish I could say that this was a deliberate and directed creative effort, but I was experimentally fumbling around with some parameters and kind of stumbled something that produced good results. Rather worryingly, most of my development works like that 
Advantages:
- It’s randomly generated, so infinite variations
- It’s animated
- It’s infinitely tileable without repetitions, if necessary
Disadvantages:
- Requires some heavy alpha blending, so fillrate-limited GPUs might struggle. Some benchmarking is needed.
A few random animated samples below. Hopefully YouTube won’t destroy the quality:
I’ve also tried tweaking the parameters to create brighter nebulae:
Although this looks pretty, I feel that it might be too bright for the rest of the game elements. Perhaps it could be made to work with rim lighting and dark silhouettes? Will investigate.
Some more static samples:
