Very simple concept but the double jump could be used more I feel like. Honestly for a one-dev game, it's pretty nice!
Overall, there are a few things that I think could make the whole experience way better without too much work (try them on your next game and tell us how it went):
- The game is themed around two-colored worlds, but both the enemies and platforms are in the background's color. Maybe make every platform blue in the blue world, but the enemies in blue world are red. Some enemies are spikes, some are circles, and there are at least 3 shades of red used for enemies making the whole thing not very recognizable.
- The placement of the whole scene is a bit weird: we don't see the sky part of the blue world when not jumping, but when jumping the red floor is completely hidden and I landed on enemies/empty spaces I didn't know existed. To fix this it might be wise to have the camera be a bit less zoomed and fixed in place? or moving in another way I don't know. Also it's very easy to have a square out of the screen, and basically lose the level like that.
- The enemies could have cleared trajectories, maybe dotted circles showing their start and end positions with dotted lines in between? It's a detail though.
- There is a bug that I haven't seen mentioned in the comments before me: If the red cube picks up a diamond before the blue one, it sometimes locks itself in place: the blue one could go forward but not the red one.
- Something to quickly restart the game might be helpful, maybe pressing on the R key reloads the scene? Or add a pause menu, that could be nice too.
All in all, the idea is cool, some misc changes would improve the experience greatly.
Congrats on your submission, and good luck for next times!