Problem/Issue:
During a list import you noticed a couple of fields, some of which are custom fields, show up in red.
Reason/Cause:
This is because the column header you specified in the list is either not recognized or does not exist.
Fix/Solution:
To correct this, be sure you have the proper syntax for the column header. Please do the following steps in order to get access to a list of all the fields and custom fields in your Marketo instance:
Now you have access to all the fields available in your Marketo instance with the proper syntax. You can use it moving forward as a guide.