Create a message handler for the Windows Message WM_NCPAINT message. The following example paints a pixel red border around the frame of the form. Example:

type
  TForm  = class(TForm)
  private
    { Private declarations }
    procedure WMNCPaint(var Msg : TWMNCPaint); message WM_NCPAINT;
  public
    { Public declarations }
  end;
var
  Form : TForm ;
implementation
{$R *.DFM}
procedure TForm .WMNCPaint(var Msg: TWMNCPaint);
var
  dc : hDc;
  Pen : hPen;
  OldPen : hPen;
  OldBrush : hBrush;
begin
  inherited;
  dc := GetWindowDC(Handle);
  msg.Result :=  ;
  Pen := CreatePen(PS_SOLID,  , RGB(255, 0, 0));
  OldPen := SelectObject(dc, Pen);
  OldBrush := SelectObject(dc, GetStockObject(NULL_BRUSH));
  Rectangle(dc, 0,0, Form .Width, Form .Height);
  SelectObject(dc, OldBrush);
  SelectObject(dc, OldPen);
  DeleteObject(Pen);
  ReleaseDC(Handle, Canvas.Handle);
end;