How to apply theme and color in wpf Metro window application

In this example i am using Prism,unity and MahApps make sure you are also using same otherwise you will not get PrismApplication,BindableBase and MetroWindow.

 MainWindow.xaml

 <metro:MetroWindow x:Class="WpfApplication.Views.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:WpfApplication"
             mc:Ignorable="d"
             xmlns:metro="http://metro.mahapps.com/winfx/xaml/controls"
             xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
             Title="Welcome To Metro ui with Prism Unity">
     <metro:MetroWindow.RightWindowCommands>
         <metro:WindowCommands>
             <ComboBox ItemsSource="{Binding LstTheme}" SelectedItem="{Binding SelectedTheme}" Width="100" Background="Transparent" BorderBrush="Transparent">
                 <i:Interaction.Triggers>
                     <i:EventTrigger EventName="SelectionChanged">
                         <i:InvokeCommandAction Command="{Binding DataContext.ApplyThemeCommand,RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}"/>
                     </i:EventTrigger>
                 </i:Interaction.Triggers>
                 <ComboBox.ItemTemplate>
                     <DataTemplate>
                         <StackPanel Orientation="Horizontal">
                             <Ellipse Width="20" Height="20" Fill="{Binding Value}"/>
                             <TextBlock Text="{Binding Name}" Margin="5" VerticalAlignment="Center"/>
                         </StackPanel>
                     </DataTemplate>
                 </ComboBox.ItemTemplate>
             </ComboBox>
             <ComboBox ItemsSource="{Binding LstColor}" SelectedItem="{Binding SelectedColor}" Width="100" Background="Transparent" BorderBrush="Transparent">
                 <i:Interaction.Triggers>
                     <i:EventTrigger EventName="SelectionChanged">
                         <i:InvokeCommandAction Command="{Binding DataContext.ApplyColorCommand,RelativeSource={RelativeSource AncestorType={x:Type ComboBox}}}"/>
                     </i:EventTrigger>
                 </i:Interaction.Triggers>
                 <ComboBox.ItemTemplate>
                     <DataTemplate>
                         <StackPanel Orientation="Horizontal">
                             <Ellipse Width="20" Height="20" Fill="{Binding Value}"/>
                             <TextBlock Text="{Binding Name}" Margin="5" VerticalAlignment="Center"/>
                         </StackPanel>
                     </DataTemplate>
                 </ComboBox.ItemTemplate>
             </ComboBox>
         </metro:WindowCommands>


     </metro:MetroWindow.RightWindowCommands>
     <StackPanel Orientation="Vertical" HorizontalAlignment="Center" VerticalAlignment="Center">
         <!--here i used DynamicResource for Foreground/Background because i want to dynamically change the color-->
         <TextBlock Height="30" Width="200" Text="This is TextBlock" Margin="5" Foreground="{DynamicResource AccentBaseColorBrush}"/>
         <Button Content="This is Button" HorizontalAlignment="Left" Width="200" Background="{DynamicResource AccentBaseColorBrush}"/>
     </StackPanel>
 </metro:MetroWindow>

 MainWindow.xaml.cs

   public partial class MainWindow : MetroWindow
     {
         public MainWindow()
         {
             InitializeComponent();
             DataContext = new MainWindowViewModel();
         }

     }


 MainWindowViewModel.cs

 public class MainWindowViewModel : BindableBase
    {

        public MainWindowViewModel()
        {
            ApplyThemeCommand = new DelegateCommand(ApplyTheme);
            ApplyColorCommand = new DelegateCommand(ApplyColor);

            _lstTheme = new ObservableCollection<NameValue>()
            {
                new NameValue() {Name = "Light", Value = "White"},
                new NameValue() {Name = "Dark", Value = "Black"}
            };

            SelectedTheme = LstTheme[0];

            _lstColor = new ObservableCollection<NameValue>()
            {
                new NameValue() {Name = "blue", Value = "#2196F3"},
                new NameValue() {Name = "red", Value = "#e52400"},
                new NameValue() {Name = "green", Value = "#60a917"},

                new NameValue() {Name = "purple", Value = "#800080"},
                new NameValue() {Name = "orange", Value = "#fa6800"}

            };

            SelectedColor = _lstColor[0];
        }

        private void ApplyColor()
        {
            ApplyThemeColor();
        }

        private void ApplyTheme()
        {
            ApplyThemeColor();
        }
        private void ApplyThemeColor()
        {
            try
            {
                var accent = SelectedColor.Name ?? LstColor[0].Name;
                var theme = SelectedTheme.Name ?? LstTheme[0].Name;
                Accent newAccent = ThemeManager.GetAccent(accent);
                AppTheme newTheme = ThemeManager.GetAppTheme("Base" + theme);
                ThemeManager.ChangeAppStyle(Application.Current, newAccent, newTheme);
            }
            catch (System.Exception ex)
            {


            }
        }


        private ObservableCollection<NameValue> _lstTheme;

        public ObservableCollection<NameValue> LstTheme
        {
            get { return _lstTheme; }
            set { SetProperty(ref _lstTheme, value); }
        }


        private ObservableCollection<NameValue> _lstColor;

        public ObservableCollection<NameValue> LstColor
        {
            get { return _lstColor; }
            set { SetProperty(ref _lstColor, value); }
        }
        private NameValue _selectedColor;

        public NameValue SelectedColor
        {
            get { return _selectedColor; }
            set { SetProperty(ref _selectedColor, value); }
        }

        private NameValue _selectedTheme;

        public NameValue SelectedTheme
        {
            get { return _selectedTheme; }
            set { SetProperty(ref _selectedTheme, value); }
        }

        public ICommand ApplyThemeCommand { get; set; }
        public ICommand ApplyColorCommand { get; set; }

    }

 NameValue.cs

  public class NameValue : BindableBase
     {

         private string _name;

         public string Name
         {
             get { return _name; }
             set { SetProperty(ref _name, value); }
         }
         private string _value;

         public string Value
         {
             get { return _value; }
             set { SetProperty(ref _value, value); }
         }

     }


 App.xaml

 <prism:PrismApplication x:Class="WpfApplication.App"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:local="clr-namespace:WpfApplication"
              xmlns:prism="http://prismlibrary.com/">
     <Application.Resources>
         <ResourceDictionary>
             <ResourceDictionary.MergedDictionaries>

                 <!-- MahApps.Metro resource dictionaries. Make sure that all file names are Case Sensitive! -->
                 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml"/>

                 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml"/>
                 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml"/>

                 <!-- Accent and AppTheme setting -->
                 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/Blue.xaml" />
                 <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Accents/BaseLight.xaml" />
             </ResourceDictionary.MergedDictionaries>
         </ResourceDictionary>
     </Application.Resources>
 </prism:PrismApplication>

 App.xaml.cs

  public partial class App : PrismApplication
     {
         IUnityContainer _container;
         protected override Window CreateShell()
         {
             return _container.Resolve<MainWindow>();
         }
         protected override void RegisterTypes(IContainerRegistry containerRegistry)
         {
             _container = containerRegistry.GetContainer();
         }
     }