How Can I speed up my Windows Forms App?

I have a Windows Forms App, my app has the option to switch between two theme colors, so, by checking a variable it change the color of my controls, but it takes a little seconds (1-2) to change it, I want the application to change it faster. A Short example Of The code I Use:

 if (Settings.Default.Theme == false)
   {
Button 1.BackColor = Color.Gray;
 this.DefaultBackColor =               Color.Gray; 
//More Code
}