Reference TCustomColorControl

  TCustomColorControl = class(TSurfaceGraphicControl)
  protected
    { Return the selected color }
    function GetColorValue: TColorB; virtual; abstract;
    { Select a color }
    procedure SetColorValue(Value: TColorB); virtual; abstract;
    { Invoke OnChange and repaint }
    procedure Change; virtual;
    { Select the color under the mouse }
    procedure ChangeMouse(X, Y: Integer); virtual;
    procedure MouseDown(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
    procedure MouseUp(Button: TMouseButton; Shift: TShiftState; X, Y: Integer); override;
    procedure Resize; override;
    { The last mouse position used to pick a color }
    property MousePos: TPointI read FMousePos write FMousePos;
    { The selected color }
    property ColorValue: TColorB read GetColorValue write SetColorValue;
    { OnChange is invoked when the selected color changes }
    property OnChange: TNotifyEvent read FOnChange write FOnChange;
  public
    destructor Destroy; override;
  end;