Thanks, so little time for actually play testing, seems like I some minor adjustments would have gone a long way.
For that background style you need to get yourself a dust brush set/space nebula brush set/space cloud brush set from somewhere like deviant art (check that the pack is really free to use). Oil spill brushes are also great but I didn't use those here. Now you just paint these brushes down in Photoshop/Gimp and you should get some nice, premade, fairly transparent dust/nebula/oil clouds with a plausible texture/composition and since these are brush sets you'll get at least 20 of them. Thats good, you need those for variance.
Something like this:
I usually make them all white so I can easily recolor them in-engine. Which basically means I assign them colors from the palette I'm using. Then you plop them down in semi regular/semi random intervals in the background, randomizing their x,y scale, angle, sprite mirroring etc. If you are worried that you are using too many objects just use fewer, bigger ones. In RT I reposition them if the player moves to far away so they basically continue forever (I also randomize them, so if you where to return to a far off point it would likely have changed, major continuity error, don't tell anyone.) But you can do much more with them. Like changing the background and their color on the fly, or have them move and parallax if you got a system for that. For an example with slightly more elaborate usage you can check out my last jam game: https://sleeper-games.itch.io/swirl-watch Peace.