Keep selection from dropdown after page reload

I have the following on change function, which reloads the page and displays the inventory of the value selected.  but it also refreshes the dropdown list to go back to 'Select Color' i need it to retain the color that was selected prior.  Can i accomplish this with little change?  I would like to stick with my javascript function if possible.

   
function OnChange(dropdown,Product_id) 
   {
       var myindex = dropdown.selectedIndex
       var SelValue = dropdown.options[myindex].value+"";
       var baseURL = '/product_as.asp?color_id='+ SelValue + '&product_id=' + Product_id;
       top.location.href = baseURL;

       return true;
   }

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this is the sub that has my dropdown

Sub CheckProductColor(Product_id,objconn)
    Dim objRS
    Dim objComm
    Dim strConnectString 
    Dim Param
    set objComm = server.Createobject("ADODB.Command")
    set objRS = server.createobject("ADODB.Recordset")
    Set Param = server.CreateObject ("ADODB.Parameter")
    set objcomm.Activeconnection = objConn
    objcomm.CommandText = "CheckProductColor"
    objcomm.CommandType = adCmdStoredProc
    Set Param = objComm.CreateParameter("@Product_id", adBigInt, adParamInput)
    objComm.Parameters.Append Param
    Param.Value = Product_id
    set objRS = objcomm.execute
    
    if objRS.eof then EXIT SUB
    
    response.Write "<select name=""Color_id"" onchange=""OnChange(this.form.Color_id,"&Product_id&")"">"
    response.write "<option selected=""Select Color"">Select Color</option>"

    while not objRS.eof
    
    response.Write "<option value="""&clng(objRS.fields("Color_id"))&""">"&trim(objRS.fields("Color_value"))&"</option>"
    objRS.movenext
    wend
    
    response.Write "</select>"
    
    Set ObjRS = Nothing
	'Set objConn = Nothing
	Set objComm.ActiveConnection = Nothing
	Set objComm = Nothing	
	Set Param = Nothing
end Sub

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