Conditional Formatting Cells That Contain Formulas - NO VBA!

I need to apply conditional formatting to cells in a column that contain formulas, or more accurately cells that do not. I have a spreadsheet with default values in a column based on a lookup function. I need to know if the user overwrites the default and cannot use UDF's or VBA. I don't think it's possible so my alternative is to include a hidden column that does the same lookup and do the conditional format off of a comparison.
Thanks in advance

Thanks but those all use VBA. I can't use any macros.