TPanel的默认颜色存储在dfm中，读取后在Paint函数中设置刷子的颜色，然后填充整个背景

TCustomPanel = class(TCustomControl)
private
FFullRepaint: Boolean;
FParentBackgroundSet: Boolean;
procedure CMCtl3DChanged(var Message: TMessage); message CM_CTL3DCHANGED;
protected
procedure CreateParams(var Params: TCreateParams); override;
procedure Paint; override;
property Color default clBtnFace; // 设置默认颜色，如果没有改变它的颜色，不用存储在dfm中
property FullRepaint: Boolean read FFullRepaint write FFullRepaint default True;
property ParentColor default False;
procedure SetParentBackground(Value: Boolean); override;
public
property ParentBackground stored FParentBackgroundSet;
constructor Create(AOwner: TComponent); override;
function GetControlsAlignment: TAlignment; override;
end;

object Panel1: TPanel
Left = 200
Top = 232
Width = 193
Height = 153
Caption = 'Panel1'
TabOrder = 2
end

object Panel1: TPanel
Left = 200
Top = 232
Width = 193
Height = 153
Caption = 'Panel1'
Color = clYellow
TabOrder = 2
end

procedure TCustomPanel.Paint;
const
Alignments: array[TAlignment] of Longint = (DT_LEFT, DT_RIGHT, DT_CENTER);
var
Rect: TRect;
TopColor, BottomColor: TColor;
FontHeight: Integer;
Flags: Longint;

procedure AdjustColors(Bevel: TPanelBevel);
begin
TopColor := clBtnHighlight;
if Bevel = bvLowered then TopColor := clBtnShadow;
BottomColor := clBtnShadow;
if Bevel = bvLowered then BottomColor := clBtnHighlight;
end;

begin
Rect := GetClientRect;
if BevelOuter <> bvNone then
begin
AdjustColors(BevelOuter);
Frame3D(Canvas, Rect, TopColor, BottomColor, BevelWidth);
end;
Frame3D(Canvas, Rect, Color, Color, BorderWidth);
if BevelInner <> bvNone then
begin
AdjustColors(BevelInner);
Frame3D(Canvas, Rect, TopColor, BottomColor, BevelWidth);
end;
with Canvas do
begin
if not ThemeServices.ThemesEnabled or not ParentBackground then
begin
Brush.Color := Color; // 就是这里设置刷子的颜色。如果把它改成clRed，当场就会让TPanel变成红色
FillRect(Rect);
end;
Brush.Style := bsClear;
Font := Self.Font;
FontHeight := TextHeight('W');
with Rect do
begin
Top := ((Bottom + Top) - FontHeight) div 2;
Bottom := Top + FontHeight;
end;
Flags := DT_EXPANDTABS or DT_VCENTER or Alignments[FAlignment];
Flags := DrawTextBiDiModeFlags(Flags);
DrawText(Handle, PChar(Caption), -1, Rect, Flags);
end;
end;