Sperm can stay alive for 3 days maximum
Dark green means that you are most fertile in these days so if you are trying to conceive you've got to have sex in these days
(Not necessarily everyday of those days )
Keep in mind that having sex before your fertility days increases the chance of getting pregnant with a girl and sex during and after these days increases the chance of getting pregnant with a boy !
If you're referring to the bluish colored bars those are the (assumed) fertile days based on the info you entered when you first installed the app. It goes from light to dark, dark being the most fertile days. I believe sperm can survive for up to 7 days.