Create a customer search with highlight based on Reminder Days field value

1. Navigate to Lists > Search > Saved Searches > New > Customer
2. On Results tab >  Columns subtab > select Formula Numeric from Field dropdown > then set Formula value with Field=Reminder Days and Formula= {reminderdays}
3. Click Set button
4. Under Highlighting tab > Highlight if... subtab > set Condition with Filter=Formula Numeric > Field=Reminder Days > Formula={reminderdays} > Formula (Numeric)=greater than > Value=(e.g) 20 > click Set button
5. Click Set button again
6. Set the Image, Text Color, Background Color, Bold and Description
7. Provide the Search Title > then Save & Run 

Note: Reminder Days field is also not available as Criteria, you may use Formula (Numeric) also