C#

public Form1()
{
    InitializeComponent();

    var tb = new TextBox();
    tb.GotFocus += delegate (object s, EventArgs a)
    {
        (s as TextBox).BackColor = Color.Red;
    };
    tb.LostFocus += delegate(object s, EventArgs a)
    {
        (s as TextBox).BackColor = Color.Green;
    };
    Controls.Add(tb);
}

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]
They hate us for our freedom![^]