tx.cs

private void mailMerge_FieldMerged(object sender, MailMerge.FieldMergedEventArgs e)
{
    if (e.TableCell == null)
        return;

    if (e.MailMergeFieldAdapter.TypeName == MergeField.TYPE_NAME)
    {
        MergeField mergeField = e.MailMergeFieldAdapter as MergeField;
        Color cellColor;
        int value;

        if (int.TryParse(mergeField.Text, out value) == true)
        {
            if (value >= 700)
                cellColor = Color.Red;
            else if (value >= 600)
                cellColor = Color.Orange;
            else if (value >= 500)
                cellColor = Color.Yellow;
            else if (value >= 400)
                cellColor = Color.Green;
            else if (value >= 300)
                cellColor = Color.Blue;
            else if (value >= 200)
                cellColor = Color.Indigo;
            else if (value >= 100)
                cellColor = Color.Violet;
            else
                cellColor = e.TableCell.CellFormat.BackColor;

            e.TableCell.CellFormat.BackColor = cellColor;
        }
    }
}