Fun game :) Could do with some more player feedback (like showing when I hover the right place to place a tower), allow player to start the game after reading the instructions and balancing. I seemed to have found the one optimal strategy at my first try:
[Blue][Green][Orange]
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[Blue][Green][Orange]
Then I just upgraded each tower when I could. Ended up with a score of 20.000 before I got bored :)
I also couldn't figure out what "Power" was and the impact it had. Overall it felt like a good game though.