I have problem with conversion color to hexadecimal. Red underline is below System.Drawing.ColorTranslator.FromHtml("paint") and rect.Color;
Variable paint is static - for now.
In my opinion the problem is in variable's type public System.Drawing.SolidBrush Color at Rect class
 List<Rect> rects = new List<Rect>();
        rects.Add(new Rect()
        {
            Width = x,
            Height = y,
            Left = w,
            Top = h,
            Fill = (System.Windows.Media.Brush)(new BrushConverter()).ConvertFromString(paint)
        });
        foreach (Rect rect in rects)
        {
             Rectangle r = new Rectangle
             {
                 Width = rect.Width,
                 Height = rect.Width,
                 Fill = rect.Fill
             };
             Canvas.SetLeft(r, rect.Left);
            Canvas.SetTop(r, rect.Top);
            canvas.Children.Add(r);
        }
    }
class Rect
{
    public int Width { get; set; }
    public int Height { get; set; }
    public int Left { get; set; }
    public int Top { get; set; }
     public System.Windows.Media.Brush Fill { get; set; }
}
private void rectangle_Click(object sender, RoutedEventArgs e)
{
    choose r1 = new choose();
    var paint = "#FFA669D1";
    int x = int.Parse(beginx.Text);
    int y = int.Parse(beginy.Text);
    int w = int.Parse(wid.Text);
    int h = int.Parse(hei.Text);
    if (!((x > canvas.ActualWidth) || (y > canvas.ActualHeight) || (w > canvas.ActualWidth) || (h > canvas.ActualHeight)))
    {
        r1.rectangle(x, y, w, h, paint, canvas);
    }
}
 
    