When the program starts, it draws sky, grass and a hot air balloon. The user can drag the balloon up and down. Clicking anywhere creates a new hot air balloon where the user clicks. When the user drags the mouse out of the window, the colors get darker. Returning the mouse to the window restores the original colors.
Note that only the most recently created balloon can be dragged and only that balloon will change color when the user moves the mouse out of the window.