Something like this:
private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
if (e.ColumnIndex == 4)
{
var check = myDataGridView.Rows[e.RowIndex].Cells[e.ColumnIndex].Value;
if (check == null) return;
if ((bool)check == true)
{
dataGridView1[e.ColumnIndex, e.RowIndex].Style.ForeColor = Color.Green;
}
else
{
dataGridView1[e.ColumnIndex, e.RowIndex].Style.ForeColor = Color.Red;
}
}
}