Regarding the issue of attaching a ControlDesigner to a control...

[youran]

After attaching a ControlDesigner to a Button, the background of the Button becomes transparent in the designer, but the BackColor remains 240, 240, 240

[DesignerAttribute(typeof(DemoDesigner))]
    public class DemoButton : Button
    {

    }
    public class DemoDesigner : ControlDesigner
    {
        public override void Initialize(IComponent component)
        {
            base.Initialize(component);
        }
    }

[#2]

Hi @youran,

You can try below line:

demoButton.BackColor = Color.FromArgb(240, 240, 240);

Thanks & Best Regards,
AddWebSolution