Colours in the Data model Pane

In the DataModel pane of Designer, what is the significance of fields which appear in Red? The data is extracted ok as far as I can tell.
DataModel

If you add or modify a field so that it is essentially different than what it was it will be red in the designer. You need to click the Synchronise Model button to resync the data model from the mapper to the template. (It is next to the button that looks like an eye)

Regards,
S