Sometimes a drop of water appears in the queue:
You win 100 points when you empty a stack of 3 rectangles with one drop of water, e.g.:
You drop water on a stack of red, yellow and magenta, the two top colors (yellow and magenta) are mixed to red.
The resulting stack would be 2 red rectangles, but a 2 identical colors disappear, so the stack becomes empty.
You win 100 points.
If you are on a slow connection:
make sure the queue (at the top of the screen) is refreshed before you stack the next rectangle.
The game ends when all stacks are full or when you click stopstart game | high scores