private void AddUnique()
{
FormatConditionCollection conds = GetFormatCondition("E21:G22", Color.LightSalmon);
int idx = conds.AddCondition(FormatConditionType.UniqueValues);
FormatCondition cond = conds[idx];
cond.Style.BackgroundColor = Color.Yellow;
cond.Style.Pattern = BackgroundType.Solid;
Cell c = _sheet.Cells["E21"];
c.PutValue("aa");
c = _sheet.Cells["G22"];
c.PutValue("aa");
}