求解一段特殊的隔行换色代码

Question

var aRows = document.getElementById("table_id").rows;
var aColor = new Array("#F00","#000");
var n = 0;
var B = "";
for(i = 1; i < aRows.length; i++){
   if(aRows(i).cells(1) != B){
       B = aRows(i).cells(1);
       n = (n + 1) % 2;
   }
   aRows(i).style.color = aColor[n];
}

Answer 1

<style>
.red{background:#f00;color:#fff}
.blue{background:#00f;color:#fff}
</style>
请问如何实现这样的换色，按B字段相同的一种颜色。
<table border="1" width="17%" id=tab>
<tr>
<td width="50">A</td>
<td width="47">B</td>
<td>C</td>
</tr>
<tr>
<td width="50">001</td>
<td width="47">401</td>
<td>1</td>
</tr>
<tr>
<td width="50">002</td>
<td width="47">401</td>
<td>2</td>
</tr>
<tr>
<td width="50">003</td>
<td width="47">401</td>
<td>3</td>
</tr>
<tr>
<td width="50">004</td>
<td width="47">401</td>
<td>4</td>
</tr>
<tr>
<td width="50">005</td>
<td width="47">401</td>
<td>5</td>
</tr>
<tr>
<td width="50">006</td>
<td width="47">402</td>
<td>1</td>
</tr>
<tr>
<td width="50">007</td>
<td width="47">402</td>
<td>2</td>
</tr>
<tr>
<td width="50">008</td>
<td width="47">402</td>
<td>3</td>
</tr>
<tr>
<td width="50">009</td>
<td width="47">402</td>
<td>1</td>
</tr>
<tr>
<td width="50">010</td>
<td width="47">403</td>
<td>2</td>
</tr>
<tr>
<td width="50">011</td>
<td width="47">403</td>
<td>1</td>
</tr>
</table><script language="javascript">
<!--
var tr=document.getElementById("tab").rows
var colorName=["red","blue"]
var colorSW=0
tr(1).className=colorName[colorSW]
for(i=2;i<tr.length;i++){
if(tr(i).cells(1).innerHTML!=tr(i-1).cells(1).innerHTML){
colorSW++
if (colorSW>=2)colorSW=0
}
tr(i).className=colorName[colorSW]
}
//-->
</script>