Need to Conditionally Set Cell Background in Classic Report

 We have a requirement that certain cells be color coded depending on some complex conditions. 

I have the logic done to determine the color to which each cell should be set. However, I am unable to figure out how to plug this into APEX.

So far, I have a query that returns the columns form a view. In addition, computed columns exist that determine the desired color of the cell. For example:

CASE 

   WHEN ( SYSDATE - RUNTIME ) > 1 THEN 'Red'

   WHEN (SYSDATE - RUNTIME ) > .5 THEN 'Yellow'

   ELSE 'Green'

END AS RUNTIME_BG

In APEX, I set these computed field to not show.