choose uniqe item from list

i have this list of colors in a wpf application.

what i want is to random choose a color each time i call the funtion but i dont want that a one color be chosen more than on time.

this is my code that not doing what i want.

 var polyline = new MapPolyline();
 polyline.Stroke = GetRandomPolylineColor();



private Brush GetRandomPolylineColor()
        {
            var brushes = new Brush[] 
            {       Brushes.Blue,
                 Brushes.Black,
                 Brushes.Red,
                 Brushes.Brown,
                 Brushes.Green,
                 Brushes.HotPink,
                 Brushes.Khaki,
                 Brushes.IndianRed,
                 Brushes.LimeGreen,
                 Brushes.Orange                               
            };

            var rnd = new Random();
            return brushes[rnd.Next(brushes.Length)];
        }