第三个下拉菜单不会从数据库中填充

我有以下Index.php：

 function getXMLHTTP() { //function to return the xml http object var xmlhttp=false; try{ xmlhttp=new XMLHttpRequest(); } catch(e) { try{ xmlhttp= new ActiveXObject("Microsoft.XMLHTTP"); } catch(e){ try{ xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); } catch(e1){ xmlhttp=false; } } } return xmlhttp; } function getColor(CategoryId) { var strURL="getColor.php?Category="+CategoryId; var req = getXMLHTTP(); if (req) { req.onreadystatechange = function() { if (req.readyState == 4) { // only if "OK" if (req.status == 200) { document.getElementById('qcolor').innerHTML=req.responseText; } else { alert("There was a problem while using XMLHTTP:\n" + req.statusText); } } } req.open("GET", strURL, true); req.send(null); } } function getBrand(CategoryId,ColorId) { var strURL="getBrand.php?Category="+CategoryId+"&Color="+ColorId; var req = getXMLHTTP(); if (req) { req.onreadystatechange = function() { if (req.readyState == 4) { // only if "OK" if (req.status == 200) { document.getElementById('qbrand').innerHTML=req.responseText; } else { alert("There was a problem while using XMLHTTP:\n" + req.statusText); } } } req.open("GET", strURL, true); req.send(null); } }    
 
 
 
Product
 
  Any Keyboard Piano  
 
Colour
 
 Select Color  
 
Brand
 
 Any   

请注意表单尚未就绪，但最后需要一个提交按钮，但是现在我只想填充下拉菜单前两个菜单工作正常，我在填写最后一个菜单时遇到问题。 getColor.php包含以下代码：

 $Category= $_GET['Category']; mysql_select_db($database_dconn, $dconn); $query="SELECT DISTINCT Color FROM products WHERE products.Category LIKE '%$Category%' AND Category!= 'Stage Pianos' AND Category!= 'Recent Pianos' AND Category!= 'Recent Keyboards' AND hidden ='no' ORDER BY Color"; $result=mysql_query($query); ?> <select name="Color" onchange="getBrand(,this.value)"> Select Color  <option value=>   

getBrand.php包含以下代码：

 $Category=$_GET['Category']; $Color=$_GET['Color']; mysql_select_db($database_dconn, $dconn); $query="SELECT DISTINCT Manufacturer FROM products WHERE products.Category LIKE '%$Category%' AND Color = '$Color' AND Category!= 'Stage Pianos' AND Category!= 'Recent Pianos' AND Category!= 'Recent Keyboards' AND hidden ='no' ORDER BY Manufacturer"; $result=mysql_query($query); ?>  Select Brand  <option value="">   

请不要担心SQL注入，因为我会对它进行排序。

不知怎的，$ Category和Color的值没有被传递到任何人看到我出错的地方？ 欢迎任何帮助