MVVM在点击时更改网格的背景颜色

我是MVVM模式的真正初学者.我正试图在按钮的点击上更改网格的背景.我有一个包含按钮的网格的xaml,以及一个ViewModel .cs,我希望在按钮点击时更改网格的背景.直到我点击时才能成功显示MessageBox ...

.xaml代码:

MainWindowViewModel.cs代码:

namespace WpfSimple
{
    class MainWindowViewModel
    {
        private ICommand m_ButtonCommand;
        public ICommand ButtonCommand
        {
            get
            {
                return m_ButtonCommand;
            }
            set
            {
                m_ButtonCommand = value;
            }
        }

        public MainWindowViewModel()
        {
            ButtonCommand=new RelayCommand(new Action