My god was that fun. That last level got me scratching my head really badly, amazing work!
I liked how polished it was regarding rules. I never encountered a state that the game hasn't thought about before.
If I can give a suggestion it would be to have a go-back action button, but most levels weren't that long to dread its absence. Also maybe having the masks and colors be consistent regarding their move in all levels would be a nice touch (by introducing new colors, that is).
All in all, it was a pleasure to play. Thank you for sharing!