Thanks for the feedback. Really good and valid points.
@greysonp: I would love to polish the color palettes even further and I was thinking to swap middle levels with the current end game levels (double colored squares) but for that I needed more feedback from other players (since for me the game became quite easy due to all the testing I did during the development). I want the game to ramp in difficulty as you progress through the levels, but if you experienced those problems in the first 4 levels, I have to address it.
@stuartlangridge: Yes, I think something minimalistic would do the trick. We've been thinking about that, but then decided to test how it would do without written instructions. Something to keep in mind if it turns out that many players have a problem figuring this out.