If a column is red within the UI, this is a required column that the end customer is enforcing to be populated. You can not submit back to the customer without populating their required columns.
You will also see required columns marked as red in the export. These columns must be populated to import and submit back to the customer.
**TIp- If you do not have all the required information for a line, you can mark that line as pending to return to that line when you have all needed information.