When you have three colors on the board (purple, green, and blue), you will notice bubbles with color inside of them. Wait until you have two different colored bubbles and click both of them. Note: Make sure you have three or more pieces of the other one.
Special pieces
Use the following special pieces as indicated.
Bubbles: Click on bubbles to detonate all similar-colored blocks on the screen.
Jellyfish: Select jellyfish to detonate the surrounding blocks. Save them for emergencies.