title: Delphi FireMonkey app can not draw simple black rectangle
body: <p>Just create simple FireMokey HD app, put TImage with align=alclient on the form and trying to draw simple black rect:</p>
  
  <pre><code>procedure TForm8.FormCreate(Sender: TObject);
  var
    c: TCanvas;
  begin
    Image.Bitmap := TBitmap.Create(ClientWidth, ClientHeight);
    c := Image.Bitmap.Canvas;
    c.BeginScene;
    try
      c.Clear(claWhite);
      c.Stroke.Color := claBlack;
      c.Stroke.Kind := TBrushKind.bkSolid;
      c.DrawRect(
        TRectF.Create(7,7,ClientWidth-7,ClientHeight-7),
        0,0,
        [],
        1
      );
    finally
      c.EndScene;
    end;
  end;
  </code></pre>
  
  <p>And it doesn't work. Color of the rect is not black, it is kind of gray.  There some changes of the color in corners. Did i need to set some other properties or what is wrong here ?
  I tried different opacity values (1,100,255,65535), picture doesn't change at all and there is no information in the help what the hell this option means.
  Zoomed left-top corner:</p>
  
  <p><img src="https://i.stack.imgur.com/3JsgE.png" alt="enter image description here"></p>
  
  <p>Also tried to use polygons as it described in example. Same problem - rounded corners and gray color instead of black (Opacity property of image is 1, all properties as by default):</p>
  
  <pre><code>procedure TForm8.Button2Click(Sender: TObject);
  var
    p1, p2, p3, p4, p5: TPointF;
    MyPolygon: TPolygon;
  begin
    // sets the points that define the polygon
    p1.Create(100, 100);
    p2.Create(200, 100);
    p3.Create(200, 200);
    p4.Create(100, 200);
    p5.Create(100, 100);
    // creates the polygon
    SetLength(MyPolygon, 5);
    MyPolygon[0] := p1;
    MyPolygon[1] := p2;
    MyPolygon[2] := p3;
    MyPolygon[3] := p4;
    MyPolygon[4] := p5;
    Image.Bitmap.Canvas.BeginScene;
    // draws the polygon on the canvas
    Image.Bitmap.Canvas.DrawPolygon(MyPolygon, 50);
    Image.Bitmap.Canvas.EndScene;
    // updates the bitmap
  //  Image.Bitmap.BitmapChanged;
   end;
  </code></pre>