Response to: How to change the color of a button on btnclick event

Revision 2
For Window Form application :

private void button3_Click(object sender, EventArgs e)
        {
            button3.BackColor = System.Drawing.Color.Black;
        }

For Web Page :

On Page level declare static variable:

static bool Isdefault= true;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                Isdefault = false;
            }
        }

and in button click event write :

protected void Button1_Click(object sender, EventArgs e)
       {
           if (!Isdefault)
           {
               Button1.BackColor = System.Drawing.Color.GreenYellow;
           }
       }