change color of the tab control panel background

Question

I have a TabControl like so:

<TabControl ItemsSource="{Binding TabItems, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                    SelectedIndex="0" 
                    BorderThickness="0" 
                    TabStripPlacement="Left"
                    Padding="10,0,0,10">
            <TabControl.ItemContainerStyle>
                <Style TargetType="TabItem">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="TabItem">
                                <Grid Name="Panel">
                                    <ContentPresenter x:Name="ContentSite" VerticalAlignment="Center" HorizontalAlignment="Center" ContentSource="Header" Margin="20,5"/>
                                </Grid>
                                <ControlTemplate.Triggers>
                                    <Trigger Property="IsSelected" Value="True">
                                        <Setter TargetName="Panel" Property="Background" Value="#d9534f" />
                                    </Trigger>
                                    <Trigger Property="IsSelected" Value="False">
                                        <Setter TargetName="Panel" Property="Background" Value="#E6E3DB" />
                                    </Trigger>
                                </ControlTemplate.Triggers>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                    <Setter Property="Header" Value="{Binding Header, Mode=OneTime}"/>
                    <Setter Property="Content" Value="{Binding Content, Mode=OneTime}"/>
                </Style>
            </TabControl.ItemContainerStyle>
        </TabControl>

Is there a way to change the color of the Panel where TabItems are located:

Thank you for any suggestions.

Answer 1

EDIT after OP clarified the question.

The are you refer to has nothing to do with the TabItem or even the TabControl. It's simply the control where the TabControl resides in.

Please see the following simple example:

<Window x:Class="StackOverflowWPF.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:local="clr-namespace:StackOverflowWPF"
        mc:Ignorable="d"
        Title="MainWindow" Height="200" Width="300">
    <Grid Background="LightSeaGreen">
        <TabControl Background="Red">
            <TabItem Header="Tab1" Background="Yellow">
            </TabItem>
            <TabItem Header="Tab1" Background="Green">
            </TabItem>
        </TabControl>
    </Grid>
</Window>

And this is what it looks like in the designer:

So going back to your example, I'm assuming you want to set the color of area pointed to by an arrow, while keeping the rest of the form in a different color. I'd make use of the Grid control for that.

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <Grid Grid.Row="0" Background="LightGreen">
        <TabControl Grid.Row="0" Background="Red" Height="100">
            <TabItem Header="Tab1" Background="Yellow">
            </TabItem>
            <TabItem Header="Tab1" Background="Green">
            </TabItem>
        </TabControl>
    </Grid>
    <Grid Grid.Row="1"/>
</Grid>

And it will look like this: