Colors "flowing" in Android background
<p>I have an application and I want to set it's background just like the Instagram's login page, the one with that "gradient colors". The colors are "moving" and it creats a cool effect. This is what I've tried so far:</p>

<pre><code>protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_take_one);
        colorFul = (RelativeLayout) findViewById(R.id.background);
        GradientDrawable gd = new GradientDrawable(GradientDrawable.Orientation.TL_BR, new int[] {a,b});
        gd.setCornerRadius(0f);
        colorFul.setBackgroundDrawable(gd);
        for(int i = 0; i&lt;6; i++){
            if(a == 0xff000000){
                a = 0xff00ffff;
                b = 0xff444444;
            }else if(a == 0xff00ffff){
                a = 0xff888888;
                b = 0xff00ff00;
            }else if(a == 0xff888888){
                a = 0xffcccccc;
                b = 0xffff00ff;
            }else if(a==0xffcccccc){
                a = 0xffff0000;
                b = 0xffffffff;
            }else if(a==0xffff0000){
                a = 0xffffffff;
                b = 0xffffff00;
            }
            System.out.println("||");
            SystemClock.sleep(1000);
            System.out.println("&gt;");
        }
    }
</code></pre>

<p>But this doesn't work. What happens is that the collors don't change, it remains black until it gets to the last <code>if</code> and then the background become white and yellow(that are, respectively, the collors 0xffffffff and 0xffffff00), in gradient shape. 
So, how can I do it? I don't care how it's done. Whether it is with GradientDrawable or using an animated gif as background(which didn't work, the gif remained still) or any other way. Thanks.
(<a href="http://i.imgur.com/TnyCQzU.gifv" rel="nofollow">This is what I want, the gif isn't that good but you can see how the background is changing it's color</a>)</p>