WPF

            <Rectangle Fill="{Binding Path=color1}" 
                       Margin="10,10,10,10" 
                       Height="Auto" Width="Auto"
                       Grid.Column="0" Grid.Row="0"
                       />      
...     

public Window2()
        {
            InitializeComponent();
            bgColors.SetColors(Colors.Green, Colors.Green, Colors.Red, Colors.Red);
            MainDockPanel.DataContext = bgColors;           
        }

internal class BGColors : INotifyPropertyChanged
    {
        private Color Color1;
        public Color color1
        {
            get { return Color1; }
            set { Color1 = value;
            NotifyPropertyChanged("color1");
            }
        }

        private Color Color2;
        public Color color2
        {
            get { return Color2; }
            set { Color2 = value;
            NotifyPropertyChanged("color2");
            }
        }

        private Color Color3;
        public Color color3
        {
            get { return Color3; }
            set
            {
                Color1 = value;
                NotifyPropertyChanged("color3");
            }
        }

        private Color Color4;
        public Color color4
        {
            get { return Color4; }
            set
            {
                Color2 = value;
                NotifyPropertyChanged("color4");
            }
        }

        public void SetColors(Color color1, Color color2, Color color3, Color color4)
        {
            this.color1 = color1;
            this.color2 = color2;
            this.color3 = color3;
            this.color4 = color4;
        }

        private void NotifyPropertyChanged(string p)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(p));
            }
        }

        public override string ToString()
        {
            return color1.ToString();
        }
  
        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }