open System open System.Drawing open System.Windows.Forms // Create form, button and add button to form let form = new Form(Text = "Hello world!") let btn = new Button(Text = "Click here") form.Controls.Add(btn) // Register event handler for button click event btn.Click.Add(fun _ -> // Generate random color and set it as background let rnd = new Random() let r, g, b = rnd.Next(256), rnd.Next(256), rnd.Next(256) form.BackColor <- Color.FromArgb(r, g, b) ) // Show the form (in F# Interactive) form.Show() // Run the application (in compiled application) Application.Run(form)