for (int i = 0; i < dataGridView1.Rows.Count; i++)
{
int x = (int)dataGridView1.Rows[i].Cells["number"].Value;
//1、2、4、5、7
if (x == 1 || x == 2 || x == 4 || x == 5 || x == 7)
{
dataGridView1.Rows[i].Cells["Columns1"].Style.BackColor = Color.Red;
}
else
{
dataGridView1.Rows[i].Cells["Columns1"].Style.BackColor = Color.Blue;
}
}