Assuming that
button1
is your button
1. Add
button1.Click +=new EventHandler(button1_Click);
after
InitializeComponent();
2. Add the method button1_Click:
private void button1_Click(object sender, EventArgs e)
{
if(button1.BackColor == Color.Red)button1.BackColor = Color.Green;
else button1.BackColor = Color.Red;
}