Bing appsetting to Panel visibility

I'm binding an app setting to a Panel visibility. I use:
<add key="Panel1_Visible" value="true"/>

and then ....

<asp:Panel ID="Panel3" runat="server" onload="Panel1_Load"
Visible="<%$ AppSettings:Panel1_Visible %>">
</asp:Panel>


Should I replace "true" with System.Boolean.TrueString?
Why this doesn't work: <add key="Panel1_Visible"
value="System.Boolean.TrueString"/>?

Thanks!