Only those blue pills contraint the hormone. Those green pills are placebos, and only are there to so you stay in the habit of taking your pill each day. Because they lack the estrogen, when taking the green pills a woman will have her period. Some women skip those green pills all together, going from one months blues to the next, thus not having their period.
Personally, I think (the opinion of a male) that doing it that way is safer, because every other month you can have a period, which isn't a bad thing. You don't want to completely skip your period.