Flickering color animation

I'm trying to animate the background color of a grid from black to white and back forever. However, the code below creates a flickering animation.

        var contentPage = new ContentPage();
        MainPage = contentPage;

        var parentGrid = new Grid();
        parentGrid.BackgroundColor = Color.Yellow;
        contentPage.Content = parentGrid;

        var grid = new Grid();
        grid.VerticalOptions = new LayoutOptions
        {
            Alignment = LayoutAlignment.Center
        };
        grid.HorizontalOptions = new LayoutOptions
        {
            Alignment = LayoutAlignment.Center
        };
        grid.BackgroundColor = Color.Black;
        grid.WidthRequest = 300;
        grid.HeightRequest = 50;
        parentGrid.Children.Add(grid);

        grid.Animate(
            name: "animate",
            animation: new Animation((val) =>
            {
                grid.BackgroundColor = (grid.BackgroundColor == Color.Black) ? Color.White : Color.Black;
            }),
            length: 3000,
            repeat: () => { return true; }
       );

I'm confused as to what length does. I assumed it was the time span the animation runs for. It's defined as uint instead of TimeSpan, so I'm not sure...
How can I remove the flashing effect and replace it with a natural animation from one color to another over the span of 3 seconds?