XAML

<mahapps:MetroWindow.Resources>
        <Ellipse x:Key="AppThemeMenuIcon"
                     x:Shared="False"
                     Width="16"
                     Height="16"
                     StrokeThickness="1"
                     Stroke="{Binding BorderColorBrush, Mode=OneWay}"
                     Fill="{Binding ColorBrush, Mode=OneWay}" />
        <Ellipse x:Key="AccentMenuIcon"
                     x:Shared="False"
                     Width="16"
                     Height="16"
                     Fill="{Binding ColorBrush, Mode=OneWay}" />

        <Style x:Key="AppThemeMenuItemStyle"
                   TargetType="{x:Type MenuItem}"
                   BasedOn="{StaticResource MetroMenuItem}">
            <Setter Property="Icon"
                        Value="{StaticResource AppThemeMenuIcon}" />
            <Setter Property="Header"
                        Value="{Binding displayName, Mode=OneWay}" />
            <Setter Property="CommandParameter" Value="{Binding Name}"/>
            <Setter Property="Command" Value="{Binding ChangeThemeCommand}"/>


        </Style>

        <Style x:Key="AccentColorMenuItemStyle"
                   TargetType="{x:Type MenuItem}"
                   BasedOn="{StaticResource MetroMenuItem}">
            <Setter Property="Icon"
                        Value="{StaticResource AccentMenuIcon}" />
            <Setter Property="Header"
                        Value="{Binding displayName, Mode=OneWay}" />
            <Setter Property="CommandParameter" Value="{Binding Name}"/>
            <Setter Property="Command" Value="{Binding ChangeAccentCommand}"/>
        </Style>
    </mahapps:MetroWindow.Resources>
    <mahapps:MetroWindow.RightWindowCommands>
        <mahapps:WindowCommands>
            <Button ToolTip="Visual Settings" Helpers:ContextMenuLeftClickBehavior.IsLeftClickEnabled="True">
                <Rectangle 
                    Width="22"
                    Height="22"
                    Fill="{Binding RelativeSource={RelativeSource AncestorType=Button}, Path=Foreground}">
                    <Rectangle.OpacityMask>
                        <VisualBrush 
                            Stretch="Uniform"
                            Visual="{StaticResource appbar_settings}">
                        </VisualBrush>
                    </Rectangle.OpacityMask>
                </Rectangle>
                <Button.ContextMenu>
                    <ContextMenu>
                        <MenuItem Header="Theme" ItemsSource="{Binding AppThemes, Mode=OneWay}" ItemContainerStyle="{StaticResource AppThemeMenuItemStyle}" />

                        <MenuItem Header="Accent" ItemsSource="{Binding AccentColors, Mode=OneWay}"  ItemContainerStyle="{StaticResource AccentColorMenuItemStyle}"/>


                    </ContextMenu>
                </Button.ContextMenu>
            </Button>
        </mahapps:WindowCommands>
    </mahapps:MetroWindow.RightWindowCommands>