Forms Data Controls :: GridView - Change Background Every Three Rows

This should not be to hard but my head is not going for it today I have a gridview that changes the sales reps name every 3 rows. The data is group in 3 rows for each rep. estimates, job & invoices each have their own row I want to change the backgroup for each rep. I am using C# and I would guess it would be in the code behind file I got this far but can not remember a way to check the next row to make sure it is the same of changed from the previous row

protected void gvSaleReport_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
string prevRep;
prevRep = e.Row.Cells[0].Text;
if (prevRep == e.Row.Cells[0].Text)
e.Row.BackColor = System.Drawing.Color.Blue;
else
e.Row.BackColor = System.Drawing.Color.White;
}
}