Change Color-TextBox Focus

<script type ="text/javascript">
function Change(obj, evt)
{
if(evt.type=="focus")
obj.style.background ="Yellow";
else if(evt.type=="blur")
obj.style.background ="White";
}

</script>
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< asp:TextBox ID="TextBox1" runat="server" onfocus ="Change(this, event)" onblur ="Change(this, event)"> </asp:TextBox >
< asp:TextBox ID="TextBox2" runat="server" onfocus ="Change(this, event)" onblur ="Change(this, event)"> </asp:TextBox>