dim nrec,i
nrec = Datagridview1.Rowcount()
for i = 0 to nrec - 1
If DataGridView1.Rows(i).Cells(7).Value < Date.Now Then
DataGridView1.Rows(i).Cells(7).Style.BackColor = Color.Red
End If
next i

Si certo ti colora sole quelle con data inferiore a quella odierna