Hey nils, good to see you!
Since it's sort of make believe.....what about making the clouds look like liquid suspended in the atmosphere. Although that probably would take some time to make it work...unless you could find or make a filter? Maybe smoother gradient in the sky/space? On human silhouettes, put a very thin inset of reflected light along 1 edge. Moon seems cliche....maybe double moon? Or star cluster? Or Earth? Or Saturn-like planet? Or lunar eclipse? Or space ship?
Just some thoughts
