Different colours of your tapelines indicate how long until your deadlines are due and help you see at a glance when your errands really require your attention.
When your tapeline is BLUE it means that the task is still too far ahead and you do not need to even think about it yet.
Once the tapeline turns ORANGE it means that your are within 7 days of the date which you set to start the notification period for the upcoming item. This is just like the "get ready" traffic light, telling you to prepare.
A GREEN tapeline means that you have progressed to the "I-want-to-be-notified" period in the course of your countdown, and it finishes on the due date, the day zero.
A RED tapeline will always have a negative number and indicate the number of days your item has been overdue.