Hi! I just played your game :)
Smart main mechanic. 👍
Could be nice to be able to use the mouse left button instead of the E key.
Also moving white/red blocks behind grey ones makes the white/red ones completely invisible. This was a bit confusing at first: I thought they completely vanished. Also it can be hard to keep track of what is behind the grey blocks. This said, the levels are short so it was not a problem but it could be if you make bigger ones.
Nice entry! ;)