It is difficult to provide a complete answer due to lack of information and code in your question. You might need something like this.
private void dataGridView1_UserDeletingRow(object sender, DataGridViewRowCancelEventArgs e)
{
e.Cancel = true;
dataGridView1.CurrentRow.DefaultCellStyle.BackColor = Color.LightGreen;
}
Follow these links. I think they maybe useful for you to solve your issue.
UserDeletingRow
event (fires when a row is about to get deleted)
DefaultCellStyle
property (to change the BackColor of the CurrentRow)