Reasons Why List-User Fields are Red

Came across this today. Putting it here in case someone else also finds this and doesn't want to spend 45 minutes to track it down.

If a User is in the App via Group and not an Individual User, the User appears as red text in List-User fields. The text is not red for User type fields. 

Not certain if this is related but the User does not receive notifications in the List-User field and does in the User type field.