How to use

Assume that we have example noesis project with view model like below...

#if UNITY_5_3_OR_NEWER
using Noesis;
using UniRxNoesisBridge;

#else
using System.Windows.Media;
#endif

namespace UI {
    /// <summary>
    /// Interaction logic for application ViewModel
    /// </summary>
    public partial class ViewModel {
        public BindableReactiveProperty<Color> TopColor { get; set; }
        //public Color TopColor { get; set; }

        public Color BottomColor { get; set; }

        public ViewModel() {
            TopColor = new BindableReactiveProperty<Color>(Color.FromRgb(16, 102, 157), "TopColor.Value");
            TopColor.Value = Color.FromRgb(16, 0, 0);
            //TopColor = Color.FromRgb(17, 102, 157);
            BottomColor = Color.FromRgb(18, 57, 87);
            int i = 0;
        }
    }
}

and code-behind of MainWindow ...

#if UNITY_5_3_OR_NEWER
#define NOESIS
using Noesis;
#else
using System;
using System.Windows;
using System.Windows.Controls;
#endif

namespace UI {
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : UserControl {
        public MainWindow() {
            InitializeComponent();

            DataContext = new ViewModel();
        }

#if NOESIS
        private void InitializeComponent() {
            Noesis.GUI.LoadComponent(this, "Assets/NoesisGUI/Sample/MainWindow.xaml");
        }
#endif
    }
}

We have to bind to <variable_name>.Value to get any messages about changed value

<UserControl x:Class="UI.MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Grid>
    <Grid.Background>
      <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
        <GradientStop Offset="0" Color="{Binding TopColor.Value}"/>
        <GradientStop Offset="1" Color="{Binding BottomColor}"/>
      </LinearGradientBrush>
    </Grid.Background>
    <Viewbox>
      <TextBlock Text="Hello World!" Foreground="White" Margin="100"/>
    </Viewbox>
  </Grid>
</UserControl>