There are 4 indicators that appear in the top right corner of the task face.
Task is New
When a new task is added to a board by another team member, you will see a green indicator in the top right corner of the task. It looks like this:
Task is Due Soon
If a task is due within 48 hours, you will see an amber indicator in the top right corner of the task. It looks like this:
Task is Due or Overdue
If a task is due today or past due, you will see a red indicator in the top right corner of the task. It looks like this: