<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
          xmlns:sys="clr-namespace:System;assembly=mscorlib"
        xmlns:local="clr-namespace:WpfApp1"    
        mc:Ignorable="d"
        Title="MainWindow" Height="720" Width="1280">
    <Window.Resources>
        <ResourceDictionary>
            <ObjectDataProvider    ObjectInstance="{x:Type Brushes}"    MethodName="GetProperties"    x:Key="Brushes" />
            <local:BrushTypeConverter  x:Key="BrushTypeConverter"></local:BrushTypeConverter>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <ComboBox Margin="0,-200,0,0"  Width="240" Height="60" ItemsSource="{Binding Source={StaticResource Brushes}}"     SelectedItem="{Binding  ForeColor}">
            <ComboBox.ItemContainerStyle>
                <Style TargetType="ComboBoxItem">
                    <Setter Property="Template" >
                        <Setter.Value>
                            <ControlTemplate TargetType="ComboBoxItem">
                                <Rectangle Width="210"  Height="46" Margin="2,2,2,2" Stroke="#cccccc" StrokeThickness="1" RadiusX="5"   RadiusY="5"  Fill="{Binding RelativeSource={x:Static RelativeSource.Self},Path=DataContext,Converter={StaticResource BrushTypeConverter}}"></Rectangle>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </ComboBox.ItemContainerStyle>
            <ComboBox.Template>
                <ControlTemplate  TargetType="ComboBox">
                    <Grid>
                        <ToggleButton  Cursor="Hand" BorderThickness="0"  BorderBrush="Transparent"  Panel.ZIndex="1"     IsChecked="{Binding Path=IsDropDownOpen, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" ClickMode="Press">
                            <ToggleButton.Template>
                                <ControlTemplate>
                                    <StackPanel Orientation="Horizontal" Background="Transparent">
                                        <Rectangle Width="210" Height="46" Margin="7,0,5,0"   Stroke="#cccccc" StrokeThickness="1" RadiusX="5"   RadiusY="5"  Fill="{Binding SelectedItem, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}},Converter={StaticResource BrushTypeConverter}}"></Rectangle>
                                        <Polyline  Grid.Column="1"  Points="0,0 5,6 10,0"   Margin="0,0,10,0"   Width="10"  Height="6"  Stretch="Fill"  Stroke="Black"  StrokeThickness="1" />
                                    </StackPanel>
                                </ControlTemplate>
                            </ToggleButton.Template>
                        </ToggleButton>
                        <Popup IsOpen="{TemplateBinding IsDropDownOpen}" Placement="Bottom" x:Name="Popup" Focusable="False" AllowsTransparency="True" PopupAnimation="Slide">
                            <Border CornerRadius="1" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{TemplateBinding ActualWidth}" x:Name="DropDown" SnapsToDevicePixels="True">
                                <ScrollViewer Margin="4,6,4,6"  MaxHeight="{TemplateBinding MaxDropDownHeight}" SnapsToDevicePixels="True" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" CanContentScroll="True">
                                    <!--StackPanel 用于显示子级，方法是将 IsItemsHost 设置为 True-->
                                    <StackPanel IsItemsHost="True" KeyboardNavigation.DirectionalNavigation="Contained" Background="White"/>
                                </ScrollViewer>
                            </Border>
                        </Popup>
                    </Grid>
                </ControlTemplate>
            </ComboBox.Template>
        </ComboBox>
    </Grid>
</Window>

public class BrushTypeConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null)
            return null;
        PropertyInfo propertyInfo = value as PropertyInfo;
        return propertyInfo.GetValue(value) as SolidColorBrush;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;
    }
}