Highlight the null cell in RadGridView

[Fadi]

Hi, I have a radGridView, the user inserts rows, i want to highlight the cell with null values.  For example to make the back  color of the cell Red.
I have tried the below code, but it did not work...

Inside a button

for (int j = 0; j < radGridView1.Rows.Count; j++)
 {
      if (radGridView1.Rows[j].Cells[4].Value.ToString() == "")
      {
             radGridView1.Rows[j].Cells[4].Style.ForeColor = Color.Red;
      }
}

So how to do it? or if there is a better highlight method that notifies the user for the empty cell.

Thanks in advance