Neat game, I enjoyed it... even though I still managed to lose even in Zen mode.
Everything fits together well in this one, and needless to say, it's all very professionally done, too. I would've liked to see some more combos, though; as far as I can tell, there were several that could be accessed with several different color combinations, and it would've been nicer to have something unique for each.
Also, after the black octopi appeared, it would've been nice to still have something to spice up the game again and change gameplay a little (not necessarily by making it more difficult, just different!) after a couple of levels. The late game felt a fair bit repetitive, although that's unlikely to be a problem if you're not playing Zen mode.
That said, well done!