public class StartGUI
{
    [CommandMethod("startplagin")]
    public static void StartPlagin()
    {
        MainView mainView = new MainView();
        autoDSK.ShowModelessWindow(mainView);
        mainView.DataContext = new ViewModel.MainViewModel();
    }
}

public class MainViewModel:INotifyPropertyChanged
    {

        #region PropertyChangedEventHandler
        /// <summary>
        /// Метод проверяющий изменилось ли свойство
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion



        private ShowLayersViewModel _showLayers;
        private ColorPickerViewModel _colorPicker;
        private string _visibleColorPicker;

        public MainViewModel()
        {
            ColorPicker = new ColorPickerViewModel();
            ShowLayers = new ShowLayersViewModel();

            //ColorPicker.VisibleColorPicker = "Collapsed";

            VisibleColorPicker = "Collapsed";
            ClickCommandVisible = new Command(arg =>
            {
                VisibleColorPicker = "Collapsed";
            });
        }

        public ShowLayersViewModel ShowLayers
        {
            get { return _showLayers; }
            set { _showLayers = value;  OnPropertyChanged("ShowLayers");}
        }

        public ColorPickerViewModel ColorPicker
        {
            get { return _colorPicker; }
            set { _colorPicker = value; OnPropertyChanged("ColorPicker"); }
        }

        public string VisibleColorPicker
        {
            get { return _visibleColorPicker; }
            set { _visibleColorPicker = value; OnPropertyChanged("VisibleColorPicker"); }
        }



        public ICommand ClickCommandVisible { get; set; }
    }

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="25" />
        <RowDefinition Height="150" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <Button Grid.Row="0" Command="{Binding ClickCommandVisible}" />
    <userControls:ShowLayers Grid.Row="1" DataContext="{Binding ShowLayers}" />
    <userControls:ColorPicker
        Grid.Row="2"
        DataContext="{Binding ColorPicker}"
        Visibility="{Binding VisibleColorPicker}" />
</Grid>