Use Navy color as theme for MahApps

App.xaml.cs

using System.Windows;
using System.Windows.Media;
using ControlzEx.Theming;

namespace WpfApp3
{
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class App : Application
    {
        protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            // add the light theme
            var lightTheme = ThemeManager.Current.AddTheme(RuntimeThemeGenerator.Current.GenerateRuntimeTheme("Light", Colors.Navy));
            // add the dark theme (not necessary if the app is only light)
            ThemeManager.Current.AddTheme(RuntimeThemeGenerator.Current.GenerateRuntimeTheme("Dark", Colors.Navy));

            // set the app to the added light theme
            ThemeManager.Current.ChangeTheme(this, lightTheme);
        }
    }
}