private void AddIconSet12()
{
FormatConditionCollection conds = GetFormatCondition("M21:O22", Color.Brown);
int idx = conds.AddCondition(FormatConditionType.IconSet);
FormatCondition cond = conds[idx];
cond.IconSet.Type = IconSetType.RedToBlack4;
Cell c = _sheet.Cells["M21"];
c.PutValue("RedToBlack4");
}
// This method implements the IconSet conditional formatting type with 3 Signs attribute.