Conditional Formatting

Replace your first line of code with:

    Selection.FormatConditions.Add Type:=xlExpression, Formula1:= _
        "=""OR(" & Replace(Selection.Range("A1").Address, "$", "") & "<$L$31*$R$31," &  Replace(Selection.Range("A1").Address, "$", "")  & ">$L$31*$Q$31)"""

I have not tested this but would be happy to do so if you provide your file.