高手帮忙，在游戏中抓不到屏幕的颜色？(100分)

我做了一个小工具，只是想抓取屏幕某个点的颜色，使用如下的代码，现发现在某些游戏中抓色时，移动鼠标，在颜色显示框中颜色的值和0交替显示，但是鼠标一停，就显示为0，不知道为什么，请各位高手帮忙看看，这段代码需要怎么改进啊？请指点一下，先谢谢了!

unit main;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, StdCtrls;

type
TForm1 = class(TForm)
Shape1: TShape;
Label1: TLabel;
Label2: TLabel;
Edit1: TEdit;
Edit2: TEdit;
Timer1: TTimer;
Button1: TButton;
Button2: TButton;
Label3: TLabel;
Edit3: TEdit;
Label4: TLabel;
Edit4: TEdit;
Label5: TLabel;
Edit5: TEdit;
procedure Button1Click(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
procedure Button2Click(Sender: TObject);
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;
p: tpoint;
hhook: integer;
hd: thandle;
yanse: integer;
h:thandle;


implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
timer1.Enabled :=true;
end;

procedure TForm1.Timer1Timer(Sender: TObject);

begin
GetCursorPos(p);
edit1.Text:=inttostr(p.X );
edit2.text:=inttostr(p.Y );
h:=windowfrompoint(p);
edit4.Text:=inttostr(h);
hd:=getdc(0);

edit5.text:=inttostr(hd);
screentoclient(p);
yanse:=getpixel(hd,p.X,p.Y);
releasedc(0,hd);
edit3.Text:=inttostr(yanse);
shape1.Brush.Color:=yanse;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
timer1.Enabled :=false;

end;

procedure TForm1.FormCreate(Sender: TObject);
begin

SetWindowPos(Form1.handle, HWND_TOPMOST,Form1.Left, Form1.Top, Form1.Width, Form1.Height,0);

end;

end.