How to update Dynamic Resource within a Dynamic Resource?

Question

I have a visual brush which is a group of shapes, the main colour of which is a dynamic resource itself - so the shape is for example MyShape and the Colour, MyColour which is referenced by the Shape object.
My problem is when I update the colour for this - it only happens the first time the shape is loaded (the colour needs to be set first) however as much as I change the colour it won't update the dynamic resource that uses the colour - how do I make this work?
Just need to make a dynamic resource work within another dynamic resource and have them both update when I change the colour.
I have no idea how to get this to work - I spent time creating a colour-picker for WPF only to find I cannot change the colour of this item - 1-Tier resources work where I set the brush/colour directly but not a colour within another object or 2-Tier Resource.

Edit: My problem seems to be specific to using these in a seperate Resource / Dictionary as my program needs to access this item from a class not the Window, the main example mentioned does not work when the MyColor is in a seperate Resource.

Answer 1

Unless I misunderstand the situation, exactly what you're talking about works pretty well. I just tried it out with this Xaml:

<Window x:Class="ConditionalTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">

    <Window.Resources>
        <SolidColorBrush x:Key="MyColor" Color="Aqua" />

        <VisualBrush x:Key="MyBrush">
            <VisualBrush.Visual>
                <Ellipse Height="50" Width="100" Fill="{DynamicResource MyColor}" />
            </VisualBrush.Visual>
        </VisualBrush>
    </Window.Resources>
    <Grid Background="{DynamicResource MyBrush}">
        <Button Height="30" Width="Auto" VerticalAlignment="Center" HorizontalAlignment="Center" Content="ChangeColor" Click="Button_Click" />
    </Grid>
</Window>

And then changed the color in the click handler for that button:

private void Button_Click(object sender, RoutedEventArgs e)
{
    ((SolidColorBrush)Resources["MyColor"]).Color = Colors.Purple;
}  

And it worked like a champ.