title: RippleDrawable mask color, what is it for?
body: <p>In referring to the RippleDrawable for Android L, <a href="https://developer.android.com/reference/android/graphics/drawable/RippleDrawable.html">https://developer.android.com/reference/android/graphics/drawable/RippleDrawable.html</a>, there's a way to mask away to contain the ripple effect within the view. The masking is done as</p>
  
  <pre><code>&lt;ripple android:color="#ff0000ff"&gt;
      &lt;item android:drawable="@drawable/white" /&gt;
  &lt;/ripple&gt;
  </code></pre>
  
  <p>We could also mask it using</p>
  
  <pre><code>&lt;ripple android:color="#ff0000ff"&gt;
      &lt;item android:drawable="@drawable/black" /&gt;
  &lt;/ripple&gt;
  </code></pre>
  
  <p>As mentioned in the document, the mask layer is not drawn on the screen, but just masking away the ripple effect. I'm curious, why should one set a color (White or Black or anything) there? Is there any significant of us setting a color as the Mask, or it is indeed any value will do?</p>
  
  <p>Hopes someone enlighten... thanks!</p>