Style of crosshair lines on a 3D chart

I am trying to modify the 3D Charts > Tooltips and Hit Test 3D Charts > Series Tooltips 3D Chart example to change the colour of the tooltip crosshairs to red. By crosshairs I mean the green lines in the image attached.

I modified SeriesTooltips3DChart.xaml by adding:

    <UserControl.Resources>
        <Style x:Key="MyCrosshairOverlayStyle" TargetType="Line">
            <Setter Property="Stroke" Value="Red" />
            <Setter Property="StrokeThickness" Value="2" />
        </Style>
        <Style x:Key="MyCrosshairProjectionStyle" TargetType="t3D:CrosshairLines">
            <Setter Property="CrosshairOverlayStyle" Value="{StaticResource MyCrosshairOverlayStyle}" />
            <Setter Property="ProjectionMode" Value="Crosshair" />
        </Style>
    </UserControl.Resources>

and modifying the TooltipModifier3D element:

<t3D:TooltipModifier3D CrosshairMode="Lines" CrosshairPlanesFill="#33FF6600" CrosshairProjectionStyle="{StaticResource MyCrosshairProjectionStyle}" />

I expected this to apply the coloured lines but it did not. What have I misunderstood?