I've decided to enter this awesome challenge. There's a lot of great entries progressing fast so far. It's cool to see different working methods/progressions, despite working from the same concept art/brief.
Some WIPS below of my progress worked on during my free time.
I've adjusted the values so that we have darker values in foreground with contrast dropping as we head into background with clouds (previewed in last WIP).
The current background group of clouds are going to act as a more distant background group of clouds. After the middle ground, I plan to extend upon the 'tunnel' look for the background, highlighted as a red scribble ;) It's an idea open to change though, so I'll see how it works out for me.
Still a lot work to be done. I'm just placing my options at the moment & once I'm happy with how things are looking in general I'll then refine/paint in & blend everything more realistically. I think my space back drop could do with a little visit again, particularly the planets & star.