private void timer1_Tick(object sender, EventArgs e)

         {　　//随机变色代码

             Random rand = new Random();

             int i = rand.Next();

             i = i % ;

             switch (i) {

                 case :

                 case :

                     BackColor=Color.Red;

                     break;

                 case :

                 case :

                     BackColor=Color.Yellow;

                     break;

                 case :

                 case :

                     BackColor = Color.Green;

                     break;

              }

         }