Make a Silverlight 3 control transparent background

Need to make my Silverlight control transparent to the underlying HTML. Am doing it th开发者_运维问答e way I've seen it done before but something's not jiving...

<object data="data:application/x-silverlight-2," type="application/x-silverlight-2"
            width="640px" height="296px">
            <param name="source" value="ClientBin/slvStartPage.xap" />
            <param name="onError" value="onSilverlightError" />
            <param name="pluginbackground" value="Transparent" />
            <param name="iswindowless" value="true" />
            <param name="minRuntimeVersion" value="3.0.40624.0" />
            <param name="autoUpgrade" value="true" />
            <a href="http://go.microsoft.com/fwlink/?LinkID=149156&v=3.0.40624.0" style="text-decoration: none">
                <img src="http://go.microsoft.com/fwlink/?LinkId=108181" alt="Get Microsoft Silverlight"
                    style="border-style: none" />
            </a>
        </object>

The param names are incorrect:-

• iswindowless -> windowless
• pluginbackground -> background

Of course the control you assign to Application.RootVisual also needs a transparent background and anything else that may fill its space.