You start off with one sphere, of any color. Hovering the mouse over the sphere will slice it into 2 spheres, you can only have a maximum of 15 spheres on screen because of lag issues that I heard a lot of people having. After slicing a sphere you need to wait for it to re-grow into a whole sphere before you can slice it again. It also looks really awesome in Turbo-Mode (Shift+[click the green flag])