How To Create A Custom Accent In MahApps.Metro?

I'm trying to override the default style of the flyout. I tried to move all my styles in an own ResourceDictionary and used <Style x:Key="DefaultFlyout" TargetType="controls:Flyout" BasedOn="{StaticResource {x:Type controls:Flyout}}">, but it always ignores what I enter in BasedOn. Directly using {StaticResource Flyout} doesn't work because it's an unknown identifier, and DynamicResource isn't supported for BasedOn.

My resource dictionary Controls.xaml:

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:controls="http://metro.mahapps.com/winfx/xaml/controls">

    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />

        ... <!-- other custom resourceDictionaries -->

        <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.AnimatedSingleRowTabControl.xaml" />
    </ResourceDictionary.MergedDictionaries>
    ...
    <Style x:Key="DefaultFlyout" TargetType="controls:Flyout" BasedOn="{StaticResource {x:Type controls:Flyout}}">
        <Setter Property="Theme" Value="Accent" />
    </Style>
</ResourceDictionary>

The App.xaml where it is included:

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MyApplication;component/View/Controls.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.AnimatedSingleRowTabControl.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MyApplication;component/View/CustomAccent.xaml" />
            <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/baselight.xaml" />
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

And the part where I want to use the flyout, in MainWindow.xaml inside the <controls:FlyoutsControl>

<controls:FlyoutsControl.ItemContainerStyle>
    <Style BasedOn="{StaticResource DefaultFlyout}"
       TargetType="{x:Type controls:Flyout}">
        <Setter Property="Header"
            Value="{Binding Header}" />
        <Setter Property="IsOpen"
            Value="{Binding Visible}" />
        <Setter Property="Position"
            Value="{Binding Position, Converter={StaticResource FlyoutPositionConverter}}" />
        <Setter Property="IsModal"
            Value="{Binding IsModal}" />
    </Style>
</controls:FlyoutsControl.ItemContainerStyle>

This is the result:

It should be a blue flyout because i used <Setter Property="Theme" Value="Accent" /> but it doesn't work.

Has anyone an idea why this doesn't work? I don't really like the idea of copying the whole flyout style just to make my changes...

The problem seems to be my custom accent, but I just took the normal one and changed a few colors, this doesn't make any sense....

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:options="http://schemas.microsoft.com/winfx/2006/xaml/presentation/options"
                    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                    mc:Ignorable="options">

    <!--ACCENT COLORS-->
    <Color x:Key="HighlightColor">#FF009FDA</Color> <!-- changed -->
    <Color x:Key="AccentColor">#FF009FDA</Color> <!-- changed -->
    <Color x:Key="AccentColor2">#CC009FDA</Color> <!-- changed -->
    <Color x:Key="AccentColor3">#99009FDA</Color> <!-- changed -->
    <Color x:Key="AccentColor4">#66009FDA</Color> <!-- changed -->

    <!-- re-set brushes too -->
    <SolidColorBrush x:Key="HighlightBrush" Color="{StaticResource HighlightColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="AccentColorBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="AccentColorBrush2" Color="{StaticResource AccentColor2}" options:Freeze="True" />
    <SolidColorBrush x:Key="AccentColorBrush3" Color="{StaticResource AccentColor3}" options:Freeze="True" />
    <SolidColorBrush x:Key="AccentColorBrush4" Color="{StaticResource AccentColor4}" options:Freeze="True" />

    <SolidColorBrush x:Key="WindowTitleColorBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />

    <LinearGradientBrush x:Key="ProgressBrush" EndPoint="0.001,0.5" StartPoint="1.002,0.5" options:Freeze="True">
        <GradientStop Color="{StaticResource HighlightColor}" Offset="0" />
        <GradientStop Color="{StaticResource AccentColor3}" Offset="1" />
    </LinearGradientBrush>

    <SolidColorBrush x:Key="CheckmarkFill" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="RightArrowFill" Color="{StaticResource AccentColor}" options:Freeze="True" />

    <Color x:Key="IdealForegroundColor">White</Color>
    <SolidColorBrush x:Key="IdealForegroundColorBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="IdealForegroundDisabledBrush" Color="{StaticResource IdealForegroundColor}" Opacity="0.4" options:Freeze="True" />
    <SolidColorBrush x:Key="AccentSelectedColorBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />

    <!-- DataGrid brushes -->
    <SolidColorBrush x:Key="MetroDataGrid.HighlightBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.HighlightTextBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.MouseOverHighlightBrush" Color="{StaticResource AccentColor3}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.FocusBorderBrush" Color="{StaticResource AccentColor}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.InactiveSelectionHighlightBrush" Color="{StaticResource AccentColor2}" options:Freeze="True" />
    <SolidColorBrush x:Key="MetroDataGrid.InactiveSelectionHighlightTextBrush" Color="{StaticResource IdealForegroundColor}" options:Freeze="True" />

    <SolidColorBrush x:Key="OverlayBrush" Color="Black" Opacity="0.7"/>  <!-- added -->
</ResourceDictionary>