What are green days?
Green days are days that you are not fertile. The algorithm will distribute a green day if it has enough data to support that you are not fertile that day, either by confirming that you have already ovulated or that you are unlikely to do so within five days (due to sperm survival).
Since green days are your non-fertile days, you can have unprotected sex on green days and you do not need to use additional protection (such as a condom).*
When can I start trusting my green days?
You can trust your green days (including the very first green day you get) as long as you see it on the Today view. Please ensure to check your daily fertility status each day before having sex, and do not rely on predictions (as predictions are subject to change). Keep in mind that your daily fertility status is for that day meaning those 24 hours from midnight to midnight.
You can learn more about red and green days here and effectiveness here.
*Remember that the only contraception method that protects against STIs is the male and female condom. Should you have any reason for concern, be sure to use them regardless of fertility status.