Add alternate row background color on a matrix

For Simple tables (Tablix) the alternate color formula is:

=iif(rownumber(nothing) Mod 2, "White", "#f5f4e9")

I have a table matrix that I would like to alternate the row color, the problem is that multiple cells shift color around due to the matrix data grouping. I found  a workaround.

I will not display report data images due to data privacy, but I will explain the process as much as I can.

First; create a column in the report outside the grouping, I recomend at the end of the report; this will be our guide:

add the following expression: Remember the Field name we will call it TEXTBOX39

=iif(RunningValue(Fields!THISISTHEROWGROUPINGTHATALTERNATES.Value,CountDistinct,Nothing) Mod 2, "White", "#f5f4e9")