If you hit an octopus with the wrong-coloured paintball, it splits in two. The tutorial marks this down as something to avoid, but you can actually use it as a strategy to add more of a certain colour to the game board.
You can get to the plunger at the top of the screen by falling off the bottom. Or if you hit left and right frantically, you'll fire yourself into the air.
You can find a tutorial by hitting the spanner icon on the menu screen, then hitting the question mark. Trust us: you'll need it.