Yo!
The game is pretty cool I like the spacy vibe and even though graphics are very simple the trail players are leaving behind them feels satisfying.
There are some downsides though. I believe your intention was to create challenging game, but challenging doesn't mean unfair. Every platformer needs to be little bit forgiving or it becomes unplayable, the best example is coyote time, which is the moment when player still can jump even though it doesn't touch the platform anymore it'd really improve your game if implemented. The game requires too much of pinpoint accuracy to pass through. I couldn't pass the 3 level cause blue character was unable to jump on platform even though I had dozens attemps to try beat it, so I can't really imagine how accurate the timing should be there to jump on that platform.
But getting back to good things. I like how you slowly break the symmetry of the levels so it stops being just jumping two characters at the same time. It's good approach, first level just shows what's going on with two characters, that they both need to get through level and it's not only mirror of upper character. I don't know how much you push that symmetry break further, as I said I couldn't beat 3rd level, but first three levels looked good in that aspect.
Keep going, you're doing good.