Open up your picture in Photoshop.
Click the brush tool.
Click the arrow next to the brush in the brush tool bar and pick the brush that is named 200.
Go to Layer >> New >> Layer to make a new layer.
Click your color palette and a new screen should pop up. Pick whatever color you want.
Now on your picture, press anywhere you want to put the color bubble.
Do this multiple times with different colors if you want.