dataGridView.Columns[11].DefaultCellStyle.BackColor = Color.Wheat;
dataGridView.Columns[11].DefaultCellStyle.Font = new Font(dataGridView.Columns[10].DefaultCellStyle.Font,FontStyle.Bold);

foreach (DataGridViewRow r in dataGridView1.Rows)
            {
                r.Cells[11].Style.BackColor = Color.AliceBlue;
                r.Cells[11].Style.Font = new Font(dataGridView1.Columns[11].DefaultCellStyle.Font, FontStyle.Bold);
            }

   private void myDataGridView_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
        {
            try
            {
                if (e.ColumnIndex == thisDataGridViewTextBoxColumn.Index)
                {
                    decimal o = (decimal)thisDataGridView.Rows[e.RowIndex].Cells[myGridViewTextBoxColumn.Index].Value;
                    decimal n = (decimal)myDataGridView.Rows[e.RowIndex].Cells[anyDataGridViewTextBoxColumn.Index].Value;
                    if (o < n && o > 0)
                        e.CellStyle.ForeColor = Color.Red;

                }
            }
            catch { }
        }