Reference data is an optional way to enter the rim and inverts for all your structures. If the reference data is pre-filled, then the values will be automatically filled after you enter the coorisponding structure id during the takeoff entry.
You have the option to fill the data after your takeoff has already been drawn. The structure id, rim, and inverts will automatically be added to the reference data only if it does not exist already. If it already exists the reference data will not be updated. You can edit the reference data and then press the "Update Structure" button to push the data out to the drawn structure.
If the row is red it indicates that the id has not been assigned to any drawn structures.