<ThemedWindow ...
    xmlns:dxi="http://schemas.devexpress.com/winfx/2008/xaml/core/internal"
    xmlns:dxt="http://schemas.devexpress.com/winfx/2008/xaml/core/themekeys">
    <Grid>
        <Button Background="{dxi:ThemeResource {dxt:PaletteBrushThemeKey ResourceKey=Button.Background}}" 
                BorderBrush="{dxi:ThemeResource {dxt:PaletteBrushThemeKey ResourceKey=Border}}"  
                BorderThickness="1" />  
    </Grid>
</ThemedWindow>

private void ThemeManager_ThemeChanged(DependencyObject sender, ThemeChangedRoutedEventArgs e) {
    var resource = TryFindResource(new PaletteBrushThemeKeyExtension { ThemeName = e.ThemeName, ResourceKey = "Backstage.Background" });
    myButton.Background = (Brush)resource;
}

Private Sub ThemeManager_ThemeChanged(ByVal sender As DependencyObject, ByVal e As ThemeChangedRoutedEventArgs)
    Dim resource = TryFindResource(New PaletteBrushThemeKeyExtension With {
        .ThemeName = e.ThemeName,
        .ResourceKey = "Backstage.Background"
    })
    myButton.Background = CType(resource, Brush)
End Sub

<Window 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:local="clr-namespace:WpfApp36"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="WpfApp36.MainWindow">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <local:CustomControl1 Grid.Row="0" Margin="5" Text="Custom control binding to a theme name"/>
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls;

namespace WpfApp36 {
    public class CustomControl1 : Control {
        static CustomControl1() {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(CustomControl1), new FrameworkPropertyMetadata(typeof(CustomControl1)));
        }

        public string Text {
            get { return (string)GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }
        }
        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register("Text", typeof(string), typeof(CustomControl1), new PropertyMetadata(null));
    }
}

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:dxt="http://schemas.devexpress.com/winfx/2008/xaml/core/themekeys" 
                    xmlns:local="clr-namespace:WpfApp36">    
    <Style TargetType="{x:Type local:CustomControl1}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:CustomControl1}">
                    <Border BorderBrush="{DynamicResource {dxt:PaletteBrushThemeKey ResourceKey=Border, ThemeName=VS2017Blue}}" BorderThickness="3">
                        <TextBlock Foreground="Black" HorizontalAlignment="Center" Text="{TemplateBinding Text}" VerticalAlignment="Center"/>
                    </Border>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

<Application x:Class="WpfApp36.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="/WPFApp36;component/CustomControl1_Resources.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>