Really really like the idea of combining the colours, it's engaging both for the gaining of size but also for the many many combinations you can surely get.
Sadly I wasn't able to see it to the end as I got stuck on the level where you had to separate in mid air and jump on the other block--I couldn't quite figure that one out.
I also took quite a while at the beginning to figure out you could dash upwards to jump. I feel like a simple fix for that might just be mapping up arrow to dash up, but I understand that might also add a bit more complexity to the mechanic.
I think it could also be slightly nicer if you found a way to naturally introduce the new mechanics instead of simply explaining to the player what they need to do to proceed; but I understand that takes a real lot of time and refinement which you might not have had the time for.
Great conecept and nice execution though, and I do feel if you expanded this it could definitely be a hit!