Cannot set trigger within TabControl template in WPF - wpf

Question

I wrote a style for my TabControl. Within the TabControl I have a TextBlock and a Button. I wish to set trigger for TabItem.IsSelected such that the font colour of the text within TextBlock changed. My code below doesn't work:
<Style x:Key="_tabItemButtonStyle" BasedOn="{StaticResource MetroTabItem}" TargetType="{x:Type TabItem}">
<Setter Property="HeaderTemplate">
<Setter.Value>
<DataTemplate>
<StackPanel Name="_TabHeaderStackPanel" >
<TextBlock Text="{ Binding TabName }" Name="_TabHeaderText" Background="{ Binding TabBackColour }" FontSize="{ Binding TabFontSize }" >
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding IsSelected,
RelativeSource={RelativeSource AncestorType=TabItem}}"
Value="True">
<Setter Property="Foreground" Value="SteelBlue"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
...
The problem I suspect is with this code:
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding IsSelected,
RelativeSource={RelativeSource AncestorType=TabItem}}"
Value="True">
<Setter Property="Foreground" Value="SteelBlue"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
EDIT:
I bind my tab items to a Collection of ViewModels. So my style binding looks as following:
<TabControl x:Name="_MainTabControl" Grid.Column="1" Grid.Row="1"
SelectedIndex="0"
ItemsSource="{Binding OpenTabs}"
ItemContainerStyle="{StaticResource _tabItemButtonStyle}" />

Answer 1

I don't know what MetroTabItem is. But the other Code looks fine.
I tried it out with sample Code. And it does exactly what you describe you want to achieve.
Please check whether your Styles are correctly applied with Style={StaticResource YourStyleName} on the TabItem
Here my XAML:
<Window x:Class="WpfApplication1.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:WpfApplication1"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
</Window.Resources>
<Grid>
<Grid.Resources>
<ResourceDictionary>
<Style TargetType="{x:Type TabItem}" x:Key="TestStyle">
<Setter Property="HeaderTemplate">
<Setter.Value>
<DataTemplate>
<StackPanel Name="_TabHeaderStackPanel" >
<TextBlock Text="test" Name="_TabHeaderText" Background="{ Binding TabBackColour }" FontSize="{ Binding TabFontSize }" >
<TextBlock.Style>
<Style TargetType="TextBlock">
<Style.Triggers>
<DataTrigger Binding="{Binding IsSelected,
RelativeSource={RelativeSource AncestorType=TabItem}}"
Value="True">
<Setter Property="Foreground" Value="SteelBlue"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
<Button Content="Test"></Button>
</StackPanel></DataTemplate></Setter.Value>
</Setter>
</Style>
</ResourceDictionary>
</Grid.Resources>
<TabControl>
<TabItem Style="{StaticResource TestStyle}">
</TabItem>
<TabItem Style="{StaticResource TestStyle}">
</TabItem>
</TabControl>
</Grid>