以下为代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Threading;
using System.Drawing.Drawing2D;

namespace _1564
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            CheckForIllegalCrossThreadCalls = false;
        }
     private   Color[] colos = new Color [20] {Color.AliceBlue,Color.Aqua,Color.Aquamarine,
     Color.Azure,Color.Beige,Color.Bisque,Color.Black,Color.BlanchedAlmond,Color.Blue,
     Color.BlueViolet,Color.Brown,Color.BurlyWood,Color.CadetBlue,Color.Chartreuse,Color.Chocolate,
     Color.Coral,Color.CornflowerBlue,Color.Red,Color.RosyBrown,Color.RoyalBlue};
     private Thread td;
     private bool falge ;
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Random rd = new Random();
            Font font = new Font("黑体",40,FontStyle.Bold);
            falge = true;
            td = new Thread(() =>
            {
                while (falge)
                {
                    int i = rd.Next(0, 19);
                    int j = rd.Next(0,19);
                    g.DrawString(" 明 • 日 • 科 • 技 ", font, 
                    new SolidBrush(colos[i]), 50, 80); 
                    Thread.Sleep(3000);
                    this.BackColor = colos[j];
                    Thread.Sleep(3000);
                }
            });
            td.Start();

        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            if (td != null)
            {
                if (td.ThreadState == ThreadState.Running)
                {
                    falge = false;
                    td.Abort(); }
            }
        }
    }
}