关于表单指定条件颜色显示问题（js）

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD><BODY>
<TABLE border =1 id=aa>
<TR>
<TD>title1</TD>
<TD>title2</TD>
<TD>title3</TD>
</TR>
<TR>
<TD>1</TD>
<TD>2</TD>
<TD>3</TD>
</TR>
<TR>
<TD>21</TD>
<TD>1</TD>
<TD>3</TD>
</TR>
</TABLE>
<SCRIPT LANGUAGE="JavaScript">
<!--
var t = document.all.aa;
for(var i=1;i<t.rows.length;i++)
{
tr = t.rows[i];
if(parseFloat(tr.cells[0].innerText)>parseFloat(tr.cells[1].innerText))
{
tr.bgColor = "red";
}

}
//-->
</SCRIPT>
</BODY>
</HTML>