C# – How to implement databinding for windows custom control

If you work with Visual Studio then it is pretty easy to get persistable settings. Right click on the project in Solution Explorer and choose Properties. Select the Settings tab and click on the hyperlink if settings doesn't exist.

Use the Settings tab to create application settings. Visual Studio creates the files Settings.settings and Settings.Designer.settings that contain the singleton class Settings inherited from ApplicationSettingsBase. You can access this class from your code to read/write application settings:

Properties.Settings.Default["SomeProperty"] = "Some Value";
Properties.Settings.Default.Save(); // Saves settings in application configuration file

This technique is applicable both for console, Windows Forms, and other project types.

Note that you need to set the scope property of your settings. If you select Application scope then Settings.Default.<your property> will be read-only.

Reference: How To: Write User Settings at Run Time with C# - Microsoft Docs

Try keeping the codebehind as small as possible.
And especially: Do not put anything into a dependency-property "access-property's" setter - this code is not executed when the WPF changes the value.

Try this one:
Code-Behind:

public partial class StatusIndicator 
    : UserControl
{
    public static readonly DependencyProperty IsGreenProperty = DependencyProperty.Register("IsGreen", typeof(bool), typeof(StatusIndicator), new UIPropertyMetadata(false));

    public bool IsGreen
    {
        get
        {
            return (bool) GetValue(IsGreenProperty);
        }
        set
        {
            SetValue(IsGreenProperty, value);
        }
    }


    public StatusIndicator()
    {
        InitializeComponent();
    }
}

XAML:

<UserControl x:Class="WpfApplication1.StatusIndicator"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:WpfApplication1="clr-namespace:WpfApplication1"
    Height="300" Width="300" x:Name="this">
    <UserControl.Template>
        <ControlTemplate TargetType="{x:Type WpfApplication1:StatusIndicator}">
            <ControlTemplate.Triggers>
                <DataTrigger Binding="{Binding ElementName=this, Path=IsGreen}"
                             Value="True">
                    <DataTrigger.EnterActions>
                        <BeginStoryboard>
                            <Storyboard FillBehavior="HoldEnd">
                                <DoubleAnimation Duration="0:0:0.500"
                                                 From="0"
                                                 To="1"
                                                 Storyboard.TargetName="green"
                                                 Storyboard.TargetProperty="Opacity" />
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.EnterActions>

                    <DataTrigger.ExitActions>
                        <BeginStoryboard>
                            <Storyboard>
                                <DoubleAnimation Duration="0:0:0.500"
                                                 From="1"
                                                 To="0"
                                                 Storyboard.TargetName="green"
                                                 Storyboard.TargetProperty="Opacity" />
                            </Storyboard>
                        </BeginStoryboard>
                    </DataTrigger.ExitActions>
                </DataTrigger>
            </ControlTemplate.Triggers>

            <Grid>
                <Rectangle x:Name="red"
                           Fill="Red"/>
                <Rectangle x:Name="green"
                           Fill="Green" 
                           Opacity="0" />
            </Grid>
        </ControlTemplate>
    </UserControl.Template>
</UserControl>