This went from tricky, to difficult, to very difficult, and then finally to relatively easy. I can say with certainty that the stretch of levels from 10-14 were easily the hardest levels in the game for me, probably since I found it hardest to reason about the even (red) movement. The levels afterward provided more tangible restrictions on the possibility spaces and more deductions to make, making what needed to be done in them all the more clear; combining this with having just got over the big difficulty hump in the middle of the game, it made the final levels feel the most satisfying for me to complete. (Levels 3-9 felt the most balanced in terms of difficulty vs. introducing the player to the mechanics, so good job on that!) Overall, I found it enjoyable, if the difficulty was a little uneven, and the swap mechanic introduced a new dimension of thinking to the game's mechanics that made me feel invested in seeing more.