Select your current color clicking any of the squares at the bottom, then click the flying balls that match your current color. The more balls you click in a row the more points you will get.

Powerups
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+:
Will turn all the balls into white for a certain time, in this time you can click any ball no matter what is your current color

Clock:
Gives you extra time

Ice cube:
Freezes all the balls in the middle air for a short time