<StackPanel>
        <Border BorderBrush="Red"></Border>
        <Button Name="StartBtn" Content="Start"/>
        <Button Name="StopBtn" Content="Stop"/>
        <Label Name="DisplayLbl" Visibility="{Binding DisplaySwitch}" FontSize="200"
               HorizontalAlignment="Center" VerticalAlignment="Center"
               Content="{Binding LabelText}" Foreground="{Binding ForeColor}" />
  </StackPanel>

using PropertyChanged;
using System.Threading;
using System.Windows;
using System.Windows.Media;
using Brush = System.Windows.Media.Brush;
namespace Caliburn.Micro.Hello
    [AddINotifyPropertyChangedInterface]
    public class IndicatorLightViewModel : IViewModel
        public Visibility DisplaySwitch { get; set; } = Visibility.Hidden;
        public string LabelText { get; set; }
        public Brush ForeColor { get; set; }
        private Thread workTask;
        public IndicatorLightViewModel()
            ForeColor = new SolidColorBrush(Color.FromRgb(255, 0, 0));
        public void StartBtn()
            DisplaySwitch = Visibility.Visible;
            LabelText = "●";
            if (workTask == null || !workTask.IsAlive)
                workTask = new Thread(IndicatorLightOperation);//添加线程 
                workTask.IsBackground = true;
                workTask.Start();
        public void StopBtn()
            if (workTask == null || workTask.IsAlive)
                workTask.Abort();
            DisplaySwitch = Visibility.Hidden;
        public void IndicatorLightOperation()
            while (true)
                Execute.OnUIThread(()=>
                    if (((SolidColorBrush)ForeColor).Color.Equals(Color.FromRgb(255, 0, 0)))
                        ForeColor = new SolidColorBrush(Color.FromRgb(0, 255, 0));
                        ForeColor = new SolidColorBrush(Color.FromRgb(255, 0, 0));
                Thread.Sleep(500);

1、String转换成Color
  Color color = (Color)ColorConverter.ConvertFromString(string);
2、String转换成Brush
   BrushConverter brushConverter = new BrushConverter();
   Brush brush = (Brush)brushConverter.ConvertFromString(string);
3、Color转换成Brush
    Brush brush = new SolidColorBrush(color));
 4、Brush转换成Color有两种方法：
（1）先将Brush转成string，再转成Color。
Color color= (Color)ColorConverter.ConvertFromString(brush.ToString());
（2）将Brush转成SolidColorBrush，再取Color。
 Color color= ((SolidColorBrush)CadColor.Background).Color;