java中设置了背景颜色，为什么不能显示？

import java.awt.*;
import javax.swing.*;

public class TransAndChat extends JFrame
{

private JLabel jla=new JLabel("用户名");;
private JLabel jlb=new JLabel("主机名");
private JLabel jlc=new JLabel("IP地址");;

JPanel jpList;
JScrollPane jsp=new JScrollPane(jpList);

public TransAndChat()
{
//界面

this.setLayout(null);

jla.setBounds(30,20,40,40);
this.add(jla);

jlb.setBounds(90,20,40,40);
this.add(jlb);

jlc.setBounds(150,20,40,40);
this.add(jlc);

JPanel jpList=new JPanel();
jsp.setBounds(5,20,280,150);
jpList.setBackground(Color.blue);
this.add(jsp);

this.setTitle("Java局域网文件传输器");
this.setBounds(100,100,300,400);
this.setBackground(Color.blue);