We have achieved three thing in Tabcontrol when user click on any Tab :
1) Selected Tab Color Change to LightGreen else LightGray.
2) Changed selected Tab header to bold.
3) TabControl outline to black color.

<Window x:Class="TabControlDemo.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="TabControlDemo" Height="350" Width="525">
<Window.Resources>
<Style TargetType="TabItem">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TabItem">
<Border BorderThickness="1" BorderBrush="Black">
<Grid Name="TabPanel">
<ContentPresenter x:Name="ContentSite"
VerticalAlignment="Center"
HorizontalAlignment="Center"
ContentSource="Header"
Margin="10,2"/>
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsSelected" Value="True">
<Setter TargetName="TabPanel" Property="Background" Value="LightGreen" />
<Setter Property="FontWeight" Value="Bold" />
</Trigger>
<Trigger Property="IsSelected" Value="False">
<Setter TargetName="TabPanel" Property="Background" Value="LightGray" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<Grid Background="#98dafc">
<TabControl Margin="10" BorderThickness="0" Background="BlanchedAlmond" >
<TabItem Header="Tab1" Width="200">
<Label Content=" Tab 1 Content goes here..." />
</TabItem>
<TabItem Header="Tab2" Width="150" >
<Label Content=" Tab 2 Content goes here..." />
</TabItem>
<TabItem Header="Tab3" Width="150" >
<Label Content=" Tab 3 Content goes here..." />
</TabItem>
</TabControl>
</Grid>
</Window>