datagridview combobox c# winforms

sir,

my name is Babin raj i am a btec student ,i am also working as a freelancer i have a doubt on datagridview combobox .the problem is that when i trys to set a datasource to combobox cell dynamically the color of the combobox dropdown list changes to black color below is the code i have used

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)

{

int n = dataGridView1.CurrentCell.RowIndex;

if (dataGridView1.CurrentCell.ColumnIndex == 0)

{

var cbCell = dataGridView1.Rows[n].Cells["category"] as DataGridViewComboBoxCell;

DataTable dt = c1.ret("select category from category").Tables[0];

cbCell.DataSource = dt;

cbCell.ValueMember = "category";

cbCell.DisplayMember = "category";

cbCell.FlatStyle = FlatStyle.System;

}

please help me i have no other source to get the answer for my question i have tryed couple of code from internet but the problem is not fixed