If someone types in a value, there will no longer be a complicated formula.
You would be better off protecting that cell from editing using
Format>Cell>Protection followed by Tools>Protection>Protect Sheet.
But.....................to answer your question.
Copy/paste this UDF to a General Module in your workbook.
Function IsFormula(cell)
Application.Volatile
IsFormula = cell.HasFormula
End Function
Select the cell to change color and Format>Conditional Formatting>Formula is:
Assuming the selection to be A1
Formula is: =NOT(IsFormula(A1))
Gord Dibben MS Excel MVP