Thanks for playing everyone!
@CiderPunk: the yellow one can give energy to the cities so they can evolve! There are more detailed instructions in-game when you select "How to play" on the title screen!
@them and Sea of Goblets: Eric Matyas of soundimage.org made the music and so kind to let me use it - check out his other work, he's really good!
@marcciosilva: the humans turning hostile is my favorite mechanic in the game's design - glad you liked it!