Jak zmienić koloro brusha?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            rectangle.Fill = new SolidColorBrush(Colors.Black);
            sliders_ValueChanged(null, null);
        }

        private void sliders_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {
            rectangle.Fill = Brushes.BlueViolet;
            Color kolor = Color.FromRgb(
                (byte) sliderR.Value,
                (byte) sliderG.Value,
                (byte) sliderB.Value);
            //  rectangle.Fill = new SolidColorBrush(kolor);
            (rectangle.Fill as SolidColorBrush).Color = kolor;      
        }
    }
}

 <Window x:Class="WpfApp2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp2"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800" MinWidth="320" MinHeight="200">
    <DockPanel LastChildFill="True">
        <Slider x:Name="sliderB" Margin="10,10,10,10" Maximum="255"  DockPanel.Dock="Bottom" ValueChanged="sliders_ValueChanged" />
        <Slider x:Name="sliderG" Margin="10,10,10,10" Maximum="255" DockPanel.Dock="Bottom" ValueChanged="sliders_ValueChanged"/>
        <Slider x:Name="sliderR" Margin="10,10,10,10" Maximum="255" DockPanel.Dock="Bottom" ValueChanged="sliders_ValueChanged"/>
        <Rectangle x:Name="rectangle"  Margin="10,10,10,0" Stroke="Black"  Fill="Red" />
    </DockPanel>
</Window>

rectangle.Fill = new SolidColorBrush(kolor);