I beat the third level (3 blue blocks) and my game crashed.
I managed to break into a room on the left of the exit portal somehow though and it contained one of the darker red squares but no light red square and no combination of moves could get me out. Luckily I remembered you could rewind.
Game is so beautiful and the art style is really refreshing. Please keep making this game!

It's a really well-made puzzle game. Not sure how you did it, but the way the gameplay mechanics grow onto you is really cool. It becomes pretty natural once you get used to it, which really reminds me of the "Now you're thinking with portals" thing. Except, blue squares, I guess. Your biggest hurdle will probably be to make players understand how the mechanics work. I think once they're "in the flow", they'll like it.

Definitely a demo I'll keep on my desktop for a while, at the very least until I've cleared all the levels.

Only technical issue I found is that the game crashed when I tried to exit with escape during the game.

You've really nailed down the presentation of your game. It feels very polished.

I don't mind the art-style if this is a short-game but I'm sure you're aware it's going to put-off a lot of people.

As for the gameplay, it's not really my cup of tea. I got to the part where you find a blue square but didn't figure out what to do after. 
The font for the instructions is pretty hard to read.