How to set the default value of a DependencyProperty of type Brush

I have the following DependencyProperty which is of type Brush. I am trying to set the default value for the PatternBrushProperty.

    public Brush PatternBrush
    {
        get => (Brush)GetValue(PatternBrushProperty);
        set => SetValue(PatternBrushProperty, value);
    }

    public static readonly DependencyProperty PatternBrushProperty =
        DependencyProperty.Register("PatternBrush", typeof(Brush), typeof(MyCustomControl),
            new UIPropertyMetadata(defaultPatternBrush));

    private static SolidColorBrush defaultPatternBrush 
       =  new((Color)ColorConverter.ConvertFromString("#C5D4E3"));

When I try to execute the application, I get the following error:

System.InvalidOperationException Message='#FFC5D4E3' is not a valid value for property 'Color'.

I have tried different methods to specify the default brush but have had no success.

Is there a way to reference a SolidColorBrush in a resource dictionary to set the value?

Declare the defaultPatternBrush as readonly static field before you register the property. The following code work just fine for me:

public partial class MyCustomControl : UserControl
{
    private static readonly SolidColorBrush s_defaultPatternBrush = 
        new SolidColorBrush((Color)ColorConverter.ConvertFromString("#C5D4E3"));

    public MyCustomControl()
    {
        InitializeComponent();
    }

    public Brush PatternBrush
    {
        get => (Brush)GetValue(PatternBrushProperty);
        set => SetValue(PatternBrushProperty, value);
    }

    public static readonly DependencyProperty PatternBrushProperty =
        DependencyProperty.Register(nameof(PatternBrush), typeof(Brush), typeof(MyCustomControl),
            new PropertyMetadata(s_defaultPatternBrush));
}