Layer Depth XNA C#

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    Texture2D texture;

    Random random;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }
    protected override void Initialize()
    {
        texture = new Texture2D(GraphicsDevice, 1, 1);
        texture.SetData(new Color[] { Color.White });

        random = new Random();

        base.Initialize();
    }

    protected override void LoadContent()
    {
        spriteBatch = new SpriteBatch(GraphicsDevice);
    }

    protected override void UnloadContent()
    {
    }

    protected override void Update(GameTime gameTime)
    {
        base.Update(gameTime);
    }
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        spriteBatch.Begin(SpriteSortMode.BackToFront, BlendState.AlphaBlend);

        spriteBatch.Draw(texture, new Rectangle(100, 100, 100, 100), null, Color.Blue, 0, Vector2.Zero, SpriteEffects.None, (float)random.NextDouble());
        spriteBatch.Draw(texture, new Rectangle(150, 150, 100, 100), null, Color.Red, 0, Vector2.Zero, SpriteEffects.None, (float)random.NextDouble());

        spriteBatch.End();

        base.Draw(gameTime);
    }
}