It is an interesting concept. It was a little confusing at first, as I didn't realise that the knights stop moving once someone reaches a green square or that you need to break a wall to be allowed to travel to enable a green square. It was interesting to discover how this logic can be used to strategically manipulate the knights to desired locations.
Instructions or even tutorial levels would definitely help make the game less daunting to play. Given the number of possible move permutations, a restart button and perhaps a undo last move would be helpful too.
A novel and potentially complex puzzle game.