모든 컨트롤은 Tag가 존재한다 모든지 다넣을수 있다. 
Tag : 빈방, 넣고 싶은걸 마음대로
넣는다.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WindowsForms01
{
       public partial class Button02 : Form
       {
             public Button02()
             {
                    InitializeComponent();
             }
             private void button1_Click(object
sender, EventArgs e)
             {
                    this.BackColor = Color.Red;
                    this.Text = "Red";
             }
             private void button2_Click(object
sender, EventArgs e)
             {
                    this.BackColor = Color.Yellow;
                    this.Text = "Yellow";
             }
             private void button3_Click(object
sender, EventArgs e)
             {
                    this.Text = "blue";
                    this.BackColor = Color.Blue;
             }
             private void button6_Click(object
sender, EventArgs e)
             {
                    this.SetColor(Color.Red);
             }
             private void button5_Click(object
sender, EventArgs e)
             {
                    this.SetColor(Color.Yellow);
             }
             private void button4_Click(object
sender, EventArgs e)
             {
                    this.SetColor(Color.Blue);
             }
             private void SetColor(Color
color)
             {
                    this.BackColor =
color;
                    this.Text =
color.ToString();
             }
             private void Btn(object
sender, EventArgs e)
             {
                    //빨강, 노랑, 파랑 버튼이 모두 호출하는 이벤트 메서드
                    //문제점 : 누가 날 불렀는지???
                    //MessageBox.Show("하하");
                    //object sender : 이벤트를 발생시킨 객체(컨트롤)
                    Button btn = (Button)sender;
                    //MessageBox.Show(btn.Text);
                    if (btn.Text == "빨강")
                    {
                           this.BackColor
= Color.Red;
                    }
                    else if (btn.Text == "노랑")
                    {
                           this.BackColor
= Color.Yellow;
                    }
                    else if (btn.Text == "파랑")
                           this.BackColor
= Color.Blue;
             }
             private void Button_SetColor(object
sender, EventArgs e)
             {
                    //네번째
                    Button btn = (Button)sender;
                    this.BackColor =
btn.BackColor;
             }
             private void Button_BackColor(object
sender, EventArgs e)
             {
                    //다섯번째
                    //object sender로 어떤 버튼이 클릭 됐는지 알아온다.
                    Button btn = (Button)sender;
                    //다운 캐스팅
                    Color c = (Color)btn.Tag;
                    this.BackColor =
c;
             }
             private void Button02_Load(object
sender, EventArgs e)
             {
                    //컨트롤 초기 작업
                    this.button15.Tag
= Color.Red;
                    this.button14.Tag
= Color.Yellow;
                    this.button13.Tag
= Color.Blue;
             }
       }
}