Alternate row formatting - Conditional Formatting with row & column groups

Is there a way to use conditional formatting to alternate the background color for a Matrix table that has both a column groupand a row group?

Here are details of my table....
Row group name:  GroupbyEmployee
Column Group name:  GroupbyProjectNumber
Value:  Sum(HoursWorked)
Tablix name:  matrix1

Note, there is only one row and one column, but they are both 'groups' so I can properly get the sum of hours worked by each employee on each project. 

I have tried the following conditional formatting on the Value text box properties, but none of them give the desired result:  
=IIF(RowNumber("GroupbyEmployee") Mod 2, "White", "PaleGreen")
=IIF(RowNumber("GroupbyProjectNumber") Mod 2, "White", "PaleGreen")
=IIF(RowNumber("matrix1") Mod 2, "White", "PaleGreen")
=IIF(RowNumber(Nothing) Mod 2, "White", "PaleGreen")

None of the scopes above for RowNumber() seem to give the desired result.  I know this has something to do with the row and/or column groups.  Is there anything that will work for this specific example? 

Thanks,
Elizabeth