private void ColorRect_MouseDown(object sender, MouseButtonEventArgs e)
{
var cd = new ColorDialog();
if (cd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
{
MainCanvas.DefaultDrawingAttributes.Color = Color.FromArgb(cd.Color.A, cd.Color.R, cd.Color.G, cd.Color.B);
ColorRect.Fill = new SolidColorBrush(MainCanvas.DefaultDrawingAttributes.Color);
}
}