WPF vb.net ProgressBar that changes color upon a certain value

Question

I'm searching for this so far and none of the found answer didn't helped me. I'm really new to wpf, and i have no clue on how to accomplish that. I need to make a progressbar changes it's color upon reaching a certain value or percentage, or whatever.

Thanks in advance

Here's my code XAML

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication2"
    Title="MainWindow" Height="350" Width="525">
<Window.Resources>
    <local:MainWindow  x:Key="ProgressForegroundConverter"/>
</Window.Resources>
<StackPanel>
    <ProgressBar Margin="20"
             Value="{Binding ElementName=progress, Path=Value}"
              Foreground="{Binding RelativeSource={RelativeSource Mode=Self}, Path=Value, Converter={StaticResource ProgressForegroundConverter}}" Height="38"/>
       <Slider Name="progress" Margin="10" Minimum="0" Maximum="100"/>
</StackPanel>

app XAML

<Application x:Class="Application"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>

</Application.Resources>

vb.net

Class MainWindow

Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As CultureInfoIetfLanguageTagConverter)

    Dim progress As Double = value / 100

    Foreground = Brushes.Red

        If progress = 100D Then

            Foreground = Brushes.Green

        ElseIf progress >= 95D Then

            Foreground = Brushes.Yellow
        End If

        Return Foreground
    End Function

Public Function ConvertBack(ByVal value As Object, targetType As Type, parameter As Object, culture As CultureInfoIetfLanguageTagConverter)

    Throw New NotImplementedException()
  End Function
End Class