The purple bar represents the time of your period.
The first green bar represents the time from the end of your period until the start of your fertile time.
The first yellow bar represents the start of your fertile time. During the yellow stage, you are potentially fertile. Fertility increases each day during the yellow stage.
The first red bar represents your most fertile time of the month. Ovulation will occur sometime during the red stage. However, after ovulation occurs, you will no longer be fertile, even though you are still in the red stage.
The second green bar represents the non fertile time after your fertile time and before your period is expected to start.
The second yellow bar represents the time your period is expected to start. Once your period starts, the cycle bar will return to just showing the purple bar.
The second red bar represents that you are officially late and are most likely pregnant.