研究一下FBrush，它是从TWinControl才有的属性（可能是因为需要句柄）——发现{$R *.dfm}在运行期执行，而且很有深意，读到属性后赋值还会触发事件，这些无法在VCL代码里直接看到

定义和创建：

TWinControl = class(TControl)
private
FBrush: TBrush;
end;

constructor TWinControl.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
FObjectInstance := Classes.MakeObjectInstance(MainWndProc);
FBrush := TBrush.Create;
FBrush.Color := FColor;
FParentCtl3D := True;
FTabOrder := -1;
end;

三处使用：

procedure TWinControl.DefaultHandler(var Message);
begin
if FHandle <> 0 then
begin
with TMessage(Message) do
begin
if (Msg = WM_CONTEXTMENU) and (Parent <> nil) then
begin
Result := Parent.Perform(Msg, WParam, LParam);
if Result <> 0 then Exit;
end;
case Msg of
WM_CTLCOLORMSGBOX..WM_CTLCOLORSTATIC:
Result := SendMessage(LParam, CN_BASE + Msg, WParam, LParam);
CN_CTLCOLORMSGBOX..CN_CTLCOLORSTATIC:
begin
SetTextColor(WParam, ColorToRGB(FFont.Color));
SetBkColor(WParam, ColorToRGB(FBrush.Color));
Result := FBrush.Handle; // 使用完了，还要返回Brush的句柄。这是消息的Result，不是函数的
end;
else
if Msg = RM_GetObjectInstance then
Result := Integer(Self)
else
begin
if Msg <> WM_PAINT then
Result := CallWindowProc(FDefWndProc, FHandle, Msg, WParam, LParam);
end;
end;
if Msg = WM_SETTEXT then
SendDockNotification(Msg, WParam, LParam);
end;
end
else
inherited DefaultHandler(Message);
end;

procedure TWinControl.CMColorChanged(var Message: TMessage);
begin
inherited;
FBrush.Color := FColor; // 改变刷子的颜色
NotifyControls(CM_PARENTCOLORCHANGED);
end;

procedure TWinControl.WMNCPaint(var Message: TMessage);
const
InnerStyles: array[TBevelCut] of Integer = (0, BDR_SUNKENINNER, BDR_RAISEDINNER, 0);
OuterStyles: array[TBevelCut] of Integer = (0, BDR_SUNKENOUTER, BDR_RAISEDOUTER, 0);
EdgeStyles: array[TBevelKind] of Integer = (0, 0, BF_SOFT, BF_FLAT);
Ctl3DStyles: array[Boolean] of Integer = (BF_MONO, 0);
var
DC: HDC;
RC, RW, SaveRW: TRect;
EdgeSize: Integer;
WinStyle: Longint;
begin
{ Get window DC that is clipped to the non-client area }
if (BevelKind <> bkNone) or (BorderWidth > 0) then
begin
DC := GetWindowDC(Handle);
try
Windows.GetClientRect(Handle, RC);
GetWindowRect(Handle, RW);
MapWindowPoints(0, Handle, RW, 2);
OffsetRect(RC, -RW.Left, -RW.Top);
ExcludeClipRect(DC, RC.Left, RC.Top, RC.Right, RC.Bottom);
{ Draw borders in non-client area }
SaveRW := RW;
InflateRect(RC, BorderWidth, BorderWidth);
RW := RC;
if BevelKind <> bkNone then
begin
EdgeSize := 0;
if BevelInner <> bvNone then Inc(EdgeSize, BevelWidth);
if BevelOuter <> bvNone then Inc(EdgeSize, BevelWidth);
with RW do
begin
WinStyle := GetWindowLong(Handle, GWL_STYLE);
if beLeft in BevelEdges then Dec(Left, EdgeSize);
if beTop in BevelEdges then Dec(Top, EdgeSize);
if beRight in BevelEdges then Inc(Right, EdgeSize);
if (WinStyle and WS_VSCROLL) <> 0 then Inc(Right, GetSystemMetrics(SM_CYVSCROLL));
if beBottom in BevelEdges then Inc(Bottom, EdgeSize);
if (WinStyle and WS_HSCROLL) <> 0 then Inc(Bottom, GetSystemMetrics(SM_CXHSCROLL));
end;
DrawEdge(DC, RW, InnerStyles[BevelInner] or OuterStyles[BevelOuter],
Byte(BevelEdges) or EdgeStyles[BevelKind] or Ctl3DStyles[Ctl3D] or BF_ADJUST);
end;
IntersectClipRect(DC, RW.Left, RW.Top, RW.Right, RW.Bottom);
RW := SaveRW;
{ Erase parts not drawn }
OffsetRect(RW, -RW.Left, -RW.Top);
 Windows.FillRect(DC, RW, Brush.Handle); // 使用刷子绘制非客户区
finally
ReleaseDC(Handle, DC);
end;
end;

inherited;

if ThemeServices.ThemesEnabled and (csNeedsBorderPaint in ControlStyle) then
ThemeServices.PaintBorder(Self, False);
end;

在TForm里也有应用：

procedure TCustomForm.WMIconEraseBkgnd(var Message: TWMIconEraseBkgnd);
begin
if FormStyle = fsMDIChild then
if (FormStyle = fsMDIChild) and not (csDesigning in ComponentState) then
FillRect(Message.DC, ClientRect, Application.MainForm.Brush.Handle)
else inherited;
end;

procedure TCustomForm.CMColorChanged(var Message: TMessage);
begin
inherited;
if FCanvas <> nil then FCanvas.Brush.Color := Color;
end;

颜色改变之后，重设Brush的颜色是靠TWinControl.CMColorChanged。那么Brush第一次正确设置颜色是在何处（不是指创建TWinControl时的-16777201值）呢？经过研究，回答如下：

应该是这样的：读取窗体是运行时，不是编译时

你的窗体代码设置了color，那个是个属性，会触发属性的set方法

你说的确实有道理。不过 {$R *.dfm}到底干了哪些事情啊？看来不是简单读数据，而且也会触发事件的
关键是，运行期读取到数据以后，也要进行:=赋值的，此时就会触发Set方法，Set方法里发送CM_COLORCHANGED消息

编译器只是简单加进exe，甚至dfm错了都发现不了
经常会出现vcl版本不对，编译通过，但是dfm不对，运行出错

次序就是这样: Create --> Load Properties --> SetColor --> CM_COLORCHANGED

总结：基本明白了，确实在VCL里见不到直接的颜色赋值语句。那是因为在运行期执行{$R *.dfm}的时候，读取到新的颜色值以后，同样要要给Color属性赋值（即dfm里存储的颜色）。这样就会触发SetColor函数，从而触发CM_COLORCHANGED。整个过程被{$R *.dfm}隐藏了，在VCL里无法直接看到。但是需要注意，整个过程是在运行期完成的，不是在编译期。